Commitments (Summary of Significant Commitments) (Detail) - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016
Commitments to extend credit
Long-term Purchase Commitment
Commitments	$ 66,980	$ 67,909
Letters of credit
Long-term Purchase Commitment
Commitments	2,525	2,583
Forward contracts related to residential mortgage loans held for sale
Long-term Purchase Commitment
Commitments	1,630	1,823
Noncancelable operating lease obligations
Long-term Purchase Commitment
Commitments	575	576
Purchase obligations
Long-term Purchase Commitment
Commitments	120	57
Capital commitments for private equity investments
Long-term Purchase Commitment
Commitments	57	59
Capital expenditures
Long-term Purchase Commitment
Commitments	49	29
Capital lease obligations
Long-term Purchase Commitment
Commitments	$ 18	$ 19