Statements of Cash Flow - Parent Company Only (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016		Dec. 31, 2015		Dec. 31, 2014
Net Income (Loss) Attributable to Parent	$ 2,273	$ 1,878	[1]	$ 1,933	[2]
Gain (Loss) on Disposition of Business	(107)	0		0
Depreciation, Amortization and Accretion, Net	727	725		786
Deferred Income Tax Expense (Benefit)	344	111		21
Stock Option Compensation And Amortization Of Restricted Stock Compensation	160	126		89
Gain (Loss) on Sale of Securities, Net	108	(4)		(21)
Increase (Decrease) in Other Operating Assets	235	(800)		(407)
Increase (Decrease) in Other Operating Liabilities	(911)	(274)		(166)
Net Cash Provided by (Used in) Operating Activities, Continuing Operations	5,509	(681)		3,552
Proceeds from Maturities, Prepayments and Calls of Available-for-sale Securities	4,186	5,108		5,680
Proceeds from Sale of Available-for-sale Securities	2,854	197		2,708
Payments to Acquire Available-for-sale Securities	(8,299)	(8,610)		(9,882)
Proceeds from Divestiture of Businesses	261	0		0
Net Cash Provided by (Used in) Investing Activities, Continuing Operations	(2,885)	(11,157)		(5,316)
Proceeds from Issuance of Long-term Debt	2,844	6,705		1,351
Repayments of Long-term Debt	(4,562)	(3,231)		(5,684)
Proceeds from Issuance of Preferred Stock and Preference Stock	1,239	0		0
Payments for Repurchase of Common Stock	(1,314)	(806)		(679)
Payments for Repurchase of Warrants	0	(24)		0
Payments Related to Tax Withholding for Share-based Compensation	(39)	(48)		(36)
Proceeds from the exercise of stock options	21	25		17
Net Cash Provided by (Used in) Financing Activities, Continuing Operations	(2,135)	12,662		(866)
Cash and Cash Equivalents, Period Increase (Decrease)	489	824		(2,630)
Cash and cash equivalents	6,912	6,423		5,599		$ 8,229
Income Taxes Paid	415	813		497
Interest Paid	730	559		523
Parent Company [Member]
Net Income (Loss) Attributable to Parent	2,273	1,878		1,933
Equity in Undistributed Earnings of Subsidiaries	(1,024)	(725)		(916)
Depreciation, Amortization and Accretion, Net	5	3		6
Deferred Income Tax Expense (Benefit)	5	11		(4)
Stock Option Compensation And Amortization Of Restricted Stock Compensation	0	3		11
Gain (Loss) on Sale of Securities, Net	(1)	0		0
Increase (Decrease) in Other Operating Assets	(15)	(129)		(72)
Increase (Decrease) in Other Operating Liabilities	122	62		(28)
Net Cash Provided by (Used in) Operating Activities, Continuing Operations	1,365	1,103		930
Proceeds from Maturities, Prepayments and Calls of Available-for-sale Securities	38	49		66
Proceeds from Sale of Available-for-sale Securities	1	4		0
Payments to Acquire Available-for-sale Securities	(17)	(4)		(15)
Payments for (Proceeds from) Loans Receivable	1,298	(889)		1,042
Payments for (Proceeds from) Other Investing Activities	0	(3)		(2)
Net Cash Provided by (Used in) Investing Activities, Continuing Operations	1,320	(843)		1,091
Proceeds from (Repayments of) Short-term Debt	(211)	5		(763)
Proceeds from Issuance of Long-term Debt	9	2,005		0
Repayments of Long-term Debt	(482)	(1,784)		(29)
Proceeds from Issuance of Preferred Stock and Preference Stock	1,239	0		0
Payments for Repurchase of Common Stock	(1,314)	(806)		(679)
Payments for Repurchase of Warrants	0	(24)		0
Payments of Dividends	(723)	(564)		(539)
Payments Related to Tax Withholding for Share-based Compensation	(39)	(48)		(36)
Proceeds from the exercise of stock options	21	25		17
Net Cash Provided by (Used in) Financing Activities, Continuing Operations	(1,500)	(1,191)		(2,029)
Cash and Cash Equivalents, Period Increase (Decrease)	1,185	(931)		(8)
Cash and cash equivalents	2,869	1,684		2,615		$ 2,623
Income Taxes Paid	(489)	(886)		(499)
Income Taxes Received From (Paid To) Subsidiaries	414	812		481
Income Taxes Paid, Net	(75)	(74)		(18)
Interest Paid	$ 140	$ 135		$ 130

[1] Beginning in the second quarter of 2017, the Company realigned its business segment structure from three segments to two segments. Specifically, the Company retained the previous composition of the Wholesale Banking segment and changed the basis of presentation of the Consumer Banking and Private Wealth Management segment and Mortgage Banking segment such that those segments were combined into a single Consumer segment. Accordingly, business segment information presented for the year ended December 31, 2016 has been revised to conform to the new business segment structure and updated internal funds transfer pricing methodology for consistent presentation.

[2] Beginning in the second quarter of 2017, the Company realigned its business segment structure from three segments to two segments. Specifically, the Company retained the previous composition of the Wholesale Banking segment and changed the basis of presentation of the Consumer Banking and Private Wealth Management segment and Mortgage Banking segment such that those segments were combined into a single Consumer segment. Accordingly, business segment information presented for the year ended December 31, 2015 has been revised to conform to the new business segment structure and updated internal funds transfer pricing methodology for consistent presentation.