Consolidated Statements of Cash Flows - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
OPERATING ACTIVITIES
Net income (loss)	$ 790	$ 920	$ 907
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities:
Provision for credit losses	266	166	57
Provision (credit) for losses on LIHTC guaranteed funds	0	0	(7)
Depreciation and amortization expense, net	314	247	246
Accretion of acquired loans	116	0	0
Increase in cash surrender value of corporate-owned life insurance	(111)	(108)	(106)
Stock-based compensation expense	99	58	44
FDIC reimbursement (payments), net of FDIC expense	13	0	1
Deferred income taxes (benefit)	11	(76)	5
Proceeds from sales of loans held for sale	8,572	7,333	5,386
Originations of loans held for sale, net of repayments	(8,361)	(7,072)	(5,415)
Net losses (gains) from sale of loans held for sale	(139)	(103)	(97)
Net losses (gains) from principal investing	(20)	(51)	(78)
Net losses (gains) and writedown on OREO	4	4	3
Net losses (gains) on leased equipment	7	(6)	(35)
Net losses (gains) on sales of fixed assets	56	8	7
Net decrease (increase) in trading account assets	(79)	(38)	(12)
Direct acquisition costs	(44)	0	0
Gain on sale of Victory	0	0	(10)
Loss on sale of residual interests and deconsolidation of securitization trusts	0	0	40
Other operating activities, net	195	(151)	384
NET CASH PROVIDED BY (USED IN) OPERATING ACTIVITIES	1,689	1,131	1,320
INVESTING ACTIVITIES
Cash received (used) in acquisitions, net of cash acquired	(481)	0	(114)
Net decrease (increase) in short-term investments, excluding acquisitions	(68)	1,562	1,358
Purchases of securities available for sale	(5,718)	(4,090)	(3,797)
Proceeds from sales of securities available for sale	4,249	19	0
Proceeds from prepayments and maturities of securities available for sale	4,241	3,098	2,860
Proceeds from prepayments and maturities of held-to-maturity securities	1,627	1,102	850
Purchases of held-to-maturity securities	(6,968)	(988)	(1,109)
Purchases of other investments	(46)	(32)	(49)
Proceeds from sales of other investments	243	145	334
Proceeds from prepayments and maturities of other investments	4	8	4
Net decrease (increase) in loans, excluding acquisitions, sales and transfers	(3,580)	(2,951)	(3,296)
Proceeds from sales of portfolio loans	140	110	120
Proceeds from corporate-owned life insurance	29	46	35
Purchases of premises, equipment, and software	(145)	(75)	(97)
Proceeds from sales of premises and equipment	0	1	1
Proceeds from sales of OREO	16	22	17
Proceeds from sale of residual interests	0	0	57
Proceeds from sale of Victory	0	0	10
NET CASH PROVIDED BY (USED IN) INVESTING ACTIVITIES	(6,457)	(2,023)	(2,816)
FINANCING ACTIVITIES
Net increase (decrease) in deposits, excluding acquisitions	4,047	(952)	2,736
Net increase (decrease) in short-term borrowings	(1,294)	(93)	(879)
Net proceeds from issuance of long-term debt	2,827	3,756	1,727
Payments on long-term debt	(1,308)	(1,172)	(1,355)
Issuance of preferred shares	1,009	0	0
Repurchase of common shares	(140)	(448)	(484)
Net proceeds from reissuance of common shares	32	22	27
Cash dividends paid	(335)	(267)	(240)
NET CASH PROVIDED BY (USED IN) FINANCING ACTIVITIES	4,838	846	1,532
NET INCREASE (DECREASE) IN CASH AND DUE FROM BANKS	70	(46)	36
CASH AND DUE FROM BANKS AT BEGINNING OF YEAR	607	653	617
CASH AND DUE FROM BANKS AT END OF YEAR	677	607	653
Additional disclosures relative to cash flows:
Interest paid	429	329	298
Income taxes paid (refunded)	144	281	131
Noncash items:
Reduction of secured borrowing and related collateral	67	160	152
Loans transferred to portfolio from held for sale	10	1	19
Loans transferred to held for sale from portfolio	45	63	16
Loans transferred to other real estate owned	36	20	23
Assets acquired	35,634	0	41
Liabilities assumed	33,028	0	17
LIHTC guaranteed funds put	0	0	7
Preferred Stock [Member]
Noncash items:
Stock issued to acquire First Niagara	350	0	0
Common Stock [Member]
Noncash items:
Stock issued to acquire First Niagara	$ 2,831	$ 0	$ 0