CONSOLIDATED STATEMENTS OF CASH FLOWS (UNAUDITED) - USD ($) $ in Millions		3 Months Ended		12 Months Ended
		Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
OPERATING ACTIVITIES
Net income		$ 388	$ 320
Adjustments to reconcile net income to net cash provided by operating activities:
Provision for credit losses		78	96
Originations of mortgage loans held for sale		(614)	(655)
Proceeds from sales of mortgage loans held for sale		655	815
Purchases of commercial loans held for sale		(468)	(384)
Proceeds from sales of commercial loans held for sale		451	380
Depreciation, amortization and accretion		122	124
Mortgage servicing rights valuation (recovery) charge-off		(3)	0
Debt securities impairment		1	1
Deferred income taxes		8	39
Share-based compensation		18	18
Net gain on sales of:
Debt securities		(8)	(4)
Decrease in other assets		331	282
Decrease in other liabilities		(255)	(179)
Net cash provided by operating activities		704	853
Investment securities:
Purchases of debt securities available for sale		(1,099)	(1,705)
Proceeds from maturities and paydowns of debt securities available for sale		806	809
Proceeds from sales of debt securities available for sale		145	404
Purchases of debt securities held to maturity		0	(57)
Proceeds from maturities and paydowns of debt securities held to maturity		131	136
Purchases of equity securities, at fair value		(39)	(73)
Proceeds from sales of equity securities, at fair value		36	68
Purchases of equity securities, at cost		(157)	(98)
Proceeds from sales of equity securities, at cost		131	118
Net decrease in interest-bearing deposits in banks		50	88
Net increase in loans and leases		(1,020)	(769)
Net increase in bank-owned life insurance		(13)	(11)
Premises and equipment:
Purchases		(32)	(14)
Capitalization of software		(57)	(39)
Net cash used in investing activities		(1,118)	(1,143)
FINANCING ACTIVITIES
Net increase in deposits		641	2,308
Net decrease in federal funds purchased and securities sold under agreements to repurchase		(500)	(55)
Net decrease in other short-term borrowed funds		(1,604)	(450)
Proceeds from issuance of long-term borrowed funds		6,250	2,997
Repayments of long-term borrowed funds		(3,250)	(4,000)
Treasury stock purchased		(175)	(130)
Dividends declared and paid to common stockholders		(108)	(72)
Payments of employee tax withholding for share-based compensation		(13)	(19)
Net cash provided by financing activities		1,241	579
Increase in cash and cash equivalents	[1]	827	289
Cash and cash equivalents at beginning of period	[1]	3,032	3,704	$ 3,704
Cash and cash equivalents at end of period	[1]	$ 3,859	$ 3,993	$ 3,032

[1] Cash and cash equivalents includes cash and due from banks and interest-bearing cash and due from banks as reflected on the Consolidated Balance Sheets.