Commitments (Summary of Significant Commitments) (Detail) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Commitments to Extend Credit
Long-term Purchase Commitment
Commitments	$ 75,696	$ 70,415
Letters of Credit
Long-term Purchase Commitment
Commitments	2,137	2,041
Forward Contracts Related to Residential Mortgage LoansHeld for Sale
Long-term Purchase Commitment
Commitments	2,901	926
Purchase Obligations
Long-term Purchase Commitment
Commitments	113	126
Capital Commitments for Private Equity Investments
Long-term Purchase Commitment
Commitments	75	32
Capital Expenditures
Long-term Purchase Commitment
Commitments	$ 84	$ 45