The correct answer is D. Incorporating forward-looking factors and idiosyncratic risk exposures into stressed operational loss estimates is the most appropriate process according to the Federal Reserve's guidelines for capital planning. This approach is favored as it allows banks to create more accurate and robust stress scenarios that account for both general economic conditions and specific risks unique to the bank.

Option A is incorrect because operational risks typically have a low correlation with market risk variables. Assuming a high positive correlation would not be a conservative or acceptable practice. The document mentions that most Bank Holding Companies (BHCs) were unable to find a meaningful correlation between macroeconomic variables and operational-risk loss severity, suggesting that assuming zero correlation is a more prudent approach.

Option B is deemed a weak practice because it involves combining two different models, which can lead to unexpected jumps in estimated losses over the planning horizon. The Federal Reserve's paper on capital planning criticizes this approach, highlighting issues with roll-rate models that estimate the rate at which loans become delinquent or default over time.

Option C is also considered a weak practice as it overlooks potential seasonal patterns in operational losses. Instead of evenly distributing losses across quarters, a better method would be to estimate the expected quarterly path of losses, along with revenues and capital projections.

The document emphasizes the importance of a strong and effective capital adequacy process, which includes estimating losses, revenues, and expenses using both qualitative and quantitative methodologies. The reference to "Capital Planning at Large Bank Holding Companies: Supervisory Expectations and Range of Current Practice" by the Board of Governors of the Federal Reserve System provides further insight into the regulatory expectations for BHCs in terms of capital planning and risk assessment.