Commitments (Summary of Significant Commitments) (Detail) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Commitments to extend credit
Long-term Purchase Commitment
Commitments	$ 75,434	$ 70,415
Letters of credit
Long-term Purchase Commitment
Commitments	2,196	2,041
Forward contracts related to residential mortgage loans held for sale
Long-term Purchase Commitment
Commitments	1,009	926
Purchase obligations
Long-term Purchase Commitment
Commitments	122	126
Capital commitments for private equity investments
Long-term Purchase Commitment
Commitments	79	32
Capital expenditures
Long-term Purchase Commitment
Commitments	$ 46	$ 45