Commitments - Summary of Significant Commitments (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Commitments to extend credit
Long-term Purchase Commitment [Line Items]
Commitments	$ 79,076	$ 70,415
Letters of credit
Long-term Purchase Commitment [Line Items]
Commitments	2,219	2,041
Forward contracts related to residential mortgage loans held for sale
Long-term Purchase Commitment [Line Items]
Commitments	2,693	926
Purchase obligations
Long-term Purchase Commitment [Line Items]
Commitments	114	126
Capital commitments for private equity investments
Long-term Purchase Commitment [Line Items]
Commitments	77	32
Capital expenditures
Long-term Purchase Commitment [Line Items]
Commitments	$ 85	$ 45