Parent Company Financial Statements - Statement of Cash Flows (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Operating Activities:
Net cash provided by operating activities	$ (1,403)	$ (561)	$ (2,024)
Investing Activities:
Net decrease (increase) in interest-bearing deposits with consolidated banking subsidiary	18,185	(29,266)	(13,494)
Proceeds from sales and maturities of available-for-sale securities	28,025	36,120	37,529
Net cash provided by (used in) investing activities	24,995	(28,492)	(14,085)
Financing Activities:
Net decrease in short-term borrowings	(7,074)	1,575	(1,155)
Proceeds from issuance of long-term debt, net of issuance costs	2,983	994	2,485
Payments for long-term debt	(1,155)	(788)	(134)
Proceeds from issuance of preferred stock	742	1,470	0
Proceeds from exercises of common stock options	4	14	121
Purchases of common stock	(1,520)	(1,650)	(2,040)
Repurchases of common stock for employee tax withholding	(222)	(232)	(189)
Payments for cash dividends	(655)	(539)	(486)
Net cash (used in) provided by financing activities	(24,240)	27,688	16,739
Net (decrease) increase	(648)	(1,365)	630
Cash and due from banks at beginning of period	1,855	3,220	2,590
Cash and due from banks at end of period	1,207	1,855	3,220
Parent Company
Operating Activities:
Net cash provided by operating activities	926	1,767	2,296
Investing Activities:
Net decrease (increase) in interest-bearing deposits with consolidated banking subsidiary	295	(1,610)	(620)
Investments in consolidated banking and non-banking subsidiaries	(7,959)	(1,142)	(1,100)
Sale or repayment of investment in consolidated banking and non-banking subsidiaries	7,891	1,011	32
Net cash provided by (used in) investing activities	227	(1,741)	(1,688)
Financing Activities:
Net increase (decrease) in commercial paper	(2,485)	667	(499)
Proceeds from issuance of long-term debt, net of issuance costs	2,983	994	2,485
Payments for long-term debt	0	(750)	0
Proceeds from issuance of preferred stock	742	1,470	0
Proceeds from exercises of common stock options	4	14	121
Purchases of common stock	(1,520)	(1,650)	(2,040)
Repurchases of common stock for employee tax withholding	(222)	(232)	(189)
Payments for cash dividends	(655)	(539)	(486)
Net cash (used in) provided by financing activities	(1,153)	(26)	(608)
Net (decrease) 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