Statements of Cash Flow - Parent Company Only (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Net Income (Loss) Attributable to Parent	$ 1,774	$ 1,344	$ 1,958
Gain (Loss) on Disposition of Business	(105)	0	0
Adjustments to reconcile net income/(loss) to net cash used in by operating activities:
Deferred Income Tax Expense (Benefit)	99	495	194
Net (increase)/decrease in other assets	(51)	(533)	807
Increase (Decrease) in Other Operating Liabilities	(431)	(846)	(1,053)
Stock Option Compensation And Amortization Of Restricted Stock Compensation	54	53	62
Cash Flows from Investing Activities:
Proceeds from sales of securities available for sale	2,470	2,063	4,300
Purchases of securities available for sale	(11,039)	(9,215)	(5,814)
Proceeds from Sale of Other Real Estate	378	472	585
Net cash (used in)/provided by investing activities	(9,273)	(8,943)	4,740
Cash Flows from Financing Activities:
Net cash provided by/(used in) financing activities	13,421	1,739	(3,005)
Supplemental Disclosures:
Income Taxes Paid	380	168	607
Depreciation, Amortization and Accretion, Net	693	708	757
Gains (Losses) on Extinguishment of Debt	0	0	16
Gain (Loss) on Sale of Securities, Net	15	(2)	(1,974)
Net Cash Provided by (Used in) Operating Activities	(1,182)	4,210	2,013
Proceeds from Maturities, Prepayments and Calls of Available-for-sale Securities	4,707	5,522	7,371
Proceeds from Sale of Other Investments	59	8	0
Proceeds from Divestiture of Businesses	193	0	0
Proceeds from Issuance of Long-term Debt	2,574	1,564	4,000
Net (decrease)/increase in cash and cash equivalents	2,966	(2,994)	3,748
Cash and Cash Equivalents, at Carrying Value	8,229	5,263	8,257
Interest Paid	534	533	774
Repayments of Long-term Debt	53	155	5,772
Proceeds from Issuance of Preferred Stock and Preference Stock	496	0	438
Payments for Repurchase of Common Stock	458	150	0
Parent Company [Member]
Net Income (Loss) Attributable to Parent	1,774	1,344	1,958
Gain (Loss) on Disposition of Business	(105)	0	0
Adjustments to reconcile net income/(loss) to net cash used in by operating activities:
Deferred Income Tax Expense (Benefit)	35	74	18
Net (increase)/decrease in other assets	207	51	(188)
Increase (Decrease) in Other Operating Liabilities	7	(339)	332
Stock Option Compensation And Amortization Of Restricted Stock Compensation	21	34	35
Cash Flows from Investing Activities:
Proceeds from sales of securities available for sale	21	57	47
Purchases of securities available for sale	(26)	(25)	(68)
Capital contributions to subsidiaries	(32)	0	(150)
Proceeds from Sale of Other Real Estate	(10)	0	0
Net cash (used in)/provided by investing activities	(1,242)	1,517	834
Cash Flows from Financing Activities:
Net cash provided by/(used in) financing activities	(323)	(306)	(1,778)
Supplemental Disclosures:
Income Taxes Paid	171	55	(605)
Income taxes received/(paid) by Parent Company	(48)	(140)	16
Equity in Undistributed Earnings of Subsidiaries	(772)	(125)	(2,110)
Depreciation, Amortization and Accretion, Net	5	5	10
Gains (Losses) on Extinguishment of Debt	0	0	15
Gain (Loss) on Sale of Securities, Net	2	(2)	(6)
Net Cash Provided by (Used in) Operating Activities	1,174	1,042	64
Proceeds from Maturities, Prepayments and Calls of Available-for-sale Securities	71	55	65
Proceeds from Sale of Other Investments	59	8	0
Payments for (Proceeds from) Loans Receivable	(1,518)	1,422	940
Proceeds from Divestiture of Businesses	193	0	0
Proceeds from (Repayments of) Short-term Debt	(686)	(827)	935
Proceeds from Issuance of Long-term Debt	723	888	15
Proceeds from Stock Options Exercised	16	17	26
Payments of Dividends	(409)	(225)	(119)
Net (decrease)/increase in cash and cash equivalents	(391)	2,253	(880)
Cash and Cash Equivalents, at Carrying Value	2,623	3,014	761
Income Taxes Received From (Paid To) Subsidiaries	219	195	(621)
Interest Paid	131	112	189
Repayments of Long-term Debt	5	9	3,073
Proceeds from Issuance of Preferred Stock and Preference Stock	496	0	438
Payments for Repurchase of Common Stock	$ 458	$ 150	$ 0