Commitments (Summary of Significant Commitments) (Detail) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Commitments to Extend Credit
Long-term Purchase Commitment
Commitments	$ 66,790	$ 75,696
Letters of Credit
Long-term Purchase Commitment
Commitments	2,190	2,137
Forward Contracts Related to Residential Mortgage LoansHeld for Sale
Long-term Purchase Commitment
Commitments	3,987	2,901
Purchase Obligations
Long-term Purchase Commitment
Commitments	136	113
Capital Commitments for Private Equity Investments
Long-term Purchase Commitment
Commitments	72	75
Capital Expenditures
Long-term Purchase Commitment
Commitments	$ 101	$ 84