Parent Company Financial Statements - Statement of Cash Flows (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Operating Activities:
Net cash provided by operating activities	$ 2,290	$ (1,403)	$ (561)
Investing Activities:
Net decrease (increase) in interest-bearing deposits with consolidated banking subsidiary	4,403	18,185	(29,266)
Business acquisitions	(437)	0	0
Net cash provided by (used in) investing activities	4,230	24,995	(28,492)
Financing Activities:
Proceeds from issuance of long-term debt, net of issuance costs	1,492	2,983	994
Payments for long-term debt	(1,441)	(1,155)	(788)
Proceeds from issuance of preferred stock, net	493	742	1,470
Proceeds from exercises of common stock options	0	4	14
Purchases of common stock	(1,365)	(1,520)	(1,650)
Repurchases of common stock for employee tax withholding	(122)	(222)	(232)
Payments for cash dividends	(723)	(655)	(539)
Net cash (used in) provided by financing activities	(6,413)	(24,240)	27,688
Net increase (decrease)	107	(648)	(1,365)
Cash and due from banks at beginning of period	1,207	1,855	3,220
Cash and due from banks at end of period	1,314	1,207	1,855
Parent Company
Operating Activities:
Net cash provided by operating activities	417	926	1,767
Investing Activities:
Net decrease (increase) in interest-bearing deposits with consolidated banking subsidiary	2,100	295	(1,610)
Investments in consolidated banking and non-banking subsidiaries	(7,600)	(7,959)	(1,142)
Sale or repayment of investment in consolidated banking and non-banking subsidiaries	6,703	7,891	1,011
Business acquisitions	(395)	0	0
Net cash provided by (used in) investing activities	808	227	(1,741)
Financing Activities:
Net increase (decrease) in commercial paper	0	(2,485)	667
Proceeds from issuance of long-term debt, net of issuance costs	1,492	2,983	994
Payments for long-term debt	(1,000)	0	(750)
Proceeds from issuance of preferred stock, net	493	742	1,470
Proceeds from exercises of common stock options	0	4	14
Purchases of common stock	(1,365)	(1,520)	(1,650)
Repurchases of common stock for employee tax withholding	(122)	(222)	(232)
Payments for cash dividends	(723)	(655)	(539)
Net cash (used in) provided by financing activities	(1,225)	(1,153)	(26)
Net increase (decrease)	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