Parent Company Financial Statements - Statement of Cash Flows (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Operating Activities:
Net cash provided by operating activities	$ 3,532	$ 5,690	$ 10,175
Investing Activities:
Net decrease (increase) in interest-bearing deposits with consolidated banking subsidiary	(47,995)	4,075	(5,813)
Purchases of available-for-sale securities	(37,873)	(38,164)	(31,814)
Net cash (used in) by investing activities	(65,534)	(2,626)	(4,496)
Financing Activities:
Proceeds from issuance of long-term debt, net of issuance costs	2,489	1,495	995
Payments for long-term debt	(1,724)	(402)	(1,461)
Proceeds from issuance of preferred stock, net of issuance costs	0	0	495
Proceeds from issuance of common stock, net of issuance costs	0	0	1,150
Payments for redemption of preferred stock	(500)	(750)	0
Repurchases of common stock	(515)	(1,585)	(350)
Repurchases of common stock for employee tax withholding	(78)	(81)	(124)
Payments for cash dividends	(889)	(930)	(828)
Net cash provided by (used in) financing activities	62,167	(2,974)	(4,471)
Net increase	165	90	1,208
Cash and due from banks at beginning of period	3,302	3,212	2,004
Cash and due from banks at end of period	3,467	3,302	3,212
Parent Company
Operating Activities:
Net cash provided by operating activities	3,513	2,684	2,250
Investing Activities:
Net decrease (increase) in interest-bearing deposits with consolidated banking subsidiary	(64)	58	46
Proceeds from sales and maturities of available-for-sale securities	1,000	900	0
Purchases of available-for-sale securities	(849)	(921)	(224)
Investments in consolidated banking and non-banking subsidiaries	(7,406)	(6,165)	(4,883)
Sale or repayment of investment in consolidated banking and non-banking subsidiaries	4,999	5,345	2,472
Net cash (used in) by investing activities	(2,320)	(783)	(2,589)
Financing Activities:
Proceeds from issuance of long-term debt, net of issuance costs	2,489	1,495	996
Payments for long-term debt	(1,700)	(50)	(1,000)
Proceeds from issuance of preferred stock, net of issuance costs	0	0	495
Proceeds from issuance of common stock, net of issuance costs	0	0	1,150
Payments for redemption of preferred stock	(500)	(750)	0
Repurchases of common stock	(515)	(1,585)	(350)
Repurchases of common stock for employee tax withholding	(78)	(81)	(124)
Payments for cash dividends	(889)	(930)	(828)
Net cash provided by (used in) financing activities	(1,193)	(1,901)	339
Net increase	0	0	0
Cash and due from banks at beginning of period	0	0	0
Cash and due from banks at end of period	$ 0	$ 0	$ 0