Commitments (Summary of Significant Commitments) (Detail) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Commitments to extend credit
Long-term Purchase Commitment
Commitments	$ 66,606	$ 67,909
Letters of credit
Long-term Purchase Commitment
Commitments	2,401	2,583
Forward contracts related to residential mortgage loans held for sale
Long-term Purchase Commitment
Commitments	2,297	1,823
Noncancelable operating lease obligations
Long-term Purchase Commitment
Commitments	580	576
Purchase obligations
Long-term Purchase Commitment
Commitments	103	57
Capital commitments for private equity investments
Long-term Purchase Commitment
Commitments	52	59
Capital expenditures
Long-term Purchase Commitment
Commitments	35	29
Capital lease obligations
Long-term Purchase Commitment
Commitments	$ 15	$ 19