Commitments (Summary of Significant Commitments) (Detail) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Commitments to extend credit
Long-term Purchase Commitment
Commitments	$ 70,689	$ 68,106
Letters of credit
Long-term Purchase Commitment
Commitments	2,062	2,185
Forward contracts related to residential mortgage loans held for sale
Long-term Purchase Commitment
Commitments	955	1,284
Noncancelable operating lease obligations
Long-term Purchase Commitment
Commitments	591	568
Purchase obligations
Long-term Purchase Commitment
Commitments	108	144
Capital commitments for private equity investments
Long-term Purchase Commitment
Commitments	33	48
Capital expenditures
Long-term Purchase Commitment
Commitments	31	37
Capital lease obligations
Long-term Purchase Commitment
Commitments	$ 19	$ 26