Commitments (Summary of Significant Commitments) (Detail) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Commitments to Extend Credit
Long-term Purchase Commitment
Commitments	$ 67,909	$ 66,884
Letters of Credit
Long-term Purchase Commitment
Commitments	2,583	3,055
Forward Contracts Related to Residential Mortgage LoansHeld for Sale
Long-term Purchase Commitment
Commitments	1,823	1,330
Noncancelable Operating Lease Obligations
Long-term Purchase Commitment
Commitments	576	635
Capital Commitments for Private Equity Investments
Long-term Purchase Commitment
Commitments	59	60
Purchase Obligations
Long-term Purchase Commitment
Commitments	57	60
Capital Expenditures
Long-term Purchase Commitment
Commitments	29	30
Capital Lease Obligations
Long-term Purchase Commitment
Commitments	$ 19	$ 27