Commitments (Summary of Significant Commitments) (Detail) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Commitments to Extend Credit
Long-term Purchase Commitment
Commitments	$ 70,415	$ 68,106
Letters of Credit
Long-term Purchase Commitment
Commitments	2,041	2,185
Forward Contracts Related to Residential Mortgage LoansHeld for Sale
Long-term Purchase Commitment
Commitments	926	1,284
Noncancelable Operating Lease Obligations
Long-term Purchase Commitment
Commitments	603	568
Capital Commitments for Private Equity Investments
Long-term Purchase Commitment
Commitments	32	48
Purchase Obligations
Long-term Purchase Commitment
Commitments	126	144
Capital Expenditures
Long-term Purchase Commitment
Commitments	45	37
Capital Lease Obligations
Long-term Purchase Commitment
Commitments	$ 20	$ 26