Parent Company Financial Statements - Statement of Cash Flows (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Operating Activities:
Net cash provided by operating activities	$ 5,690	$ 10,175	$ 6,940
Investing Activities:
Net decrease (increase) in interest-bearing deposits with consolidated banking subsidiary	4,075	(5,813)	3,708
Purchases of available-for-sale securities	(38,164)	(31,814)	(34,841)
Net cash (used in) provided by investing activities	(2,626)	(4,496)	48
Financing Activities:
Proceeds from issuance of long-term debt, net of issuance costs	1,495	995	747
Payments for long-term debt	(402)	(1,461)	(493)
Proceeds from issuance of preferred stock, net of issuance costs	0	495	0
Proceeds from issuance of common stock, net of issuance costs	0	1,150	0
Payments for redemption of preferred stock	(750)	0	0
Repurchases of common stock	(1,585)	(350)	(1,292)
Repurchases of common stock for employee tax withholding	(81)	(124)	(126)
Payments for cash dividends	(930)	(828)	(768)
Net cash (used in) financing activities	(2,974)	(4,471)	(6,188)
Net increase	90	1,208	800
Cash and due from banks at beginning of period	3,212	2,004	1,204
Cash and due from banks at end of period	3,302	3,212	2,004
Parent Company
Operating Activities:
Net cash provided by operating activities	2,684	2,250	2,047
Investing Activities:
Net decrease (increase) in interest-bearing deposits with consolidated banking subsidiary	58	46	3,103
Proceeds from sales and maturities of available-for-sale securities	900	0	0
Purchases of available-for-sale securities	(921)	(224)	0
Investments in consolidated banking and non-banking subsidiaries	(6,165)	(4,883)	(7,672)
Sale or repayment of investment in consolidated banking and non-banking subsidiaries	5,345	2,472	4,216
Net increase in investments in unconsolidated affiliates	0	0	172
Net cash (used in) provided by investing activities	(783)	(2,589)	(181)
Financing Activities:
Proceeds from issuance of long-term debt, net of issuance costs	1,495	996	748
Payments for long-term debt	(50)	(1,000)	(450)
Proceeds from issuance of preferred stock, net of issuance costs	0	495	0
Proceeds from issuance of common stock, net of issuance costs	0	1,150	0
Payments for redemption of preferred stock	(750)	0	0
Repurchases of common stock	(1,585)	(350)	(1,292)
Repurchases of common stock for employee tax withholding	(81)	(124)	(104)
Payments for cash dividends	(930)	(828)	(768)
Net cash (used in) financing activities	(1,901)	339	(1,866)
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