Fair Value (Fair Value Option - Fair Value and Principal Balances) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Customer Resale Agreements [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value - Assets	$ 155	$ 207
Aggregate Unpaid Principal Balance - Assets	148	196
Difference - Assets	7	11
Trading Loans [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value - Assets	37	6
Aggregate Unpaid Principal Balance - Assets	37	6
Loans Held For Sale [Member] | Residential Mortgage [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value - Assets	1,261	1,315
Aggregate Unpaid Principal Balance - Assets	1,202	1,280
Difference - Assets	59	35
Loans Held For Sale [Member] | Commercial Mortgage [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value - Assets	893	586
Aggregate Unpaid Principal Balance - Assets	972	678
Difference - Assets	(79)	(92)
Loans Held For Sale [Member] | Performing Loans [Member] | Residential Mortgage [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value - Assets	1,236	1,298
Aggregate Unpaid Principal Balance - Assets	1,176	1,260
Difference - Assets	60	38
Loans Held For Sale [Member] | Performing Loans [Member] | Commercial Mortgage [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value - Assets	873	583
Aggregate Unpaid Principal Balance - Assets	908	669
Difference - Assets	(35)	(86)
Loans Held For Sale [Member] | Accruing loans 90 days or more past due | Residential Mortgage [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value - Assets	9	2
Aggregate Unpaid Principal Balance - Assets	9	2
Loans Held For Sale [Member] | Nonaccrual Loans [Member] | Residential Mortgage [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value - Assets	16	15
Aggregate Unpaid Principal Balance - Assets	17	18
Difference - Assets	(1)	(3)
Loans Held For Sale [Member] | Nonaccrual Loans [Member] | Commercial Mortgage [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value - Assets	20	3
Aggregate Unpaid Principal Balance - Assets	64	9
Difference - Assets	(44)	(6)
Loans - Portfolio [Member] | Residential Mortgage [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value - Assets	1,034	1,150
Aggregate Unpaid Principal Balance - Assets	1,278	1,556
Difference - Assets	(244)	(406)
Loans - Portfolio [Member] | Performing Loans [Member] | Residential Mortgage [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value - Assets	194	233
Aggregate Unpaid Principal Balance - Assets	256	332
Difference - Assets	(62)	(99)
Loans - Portfolio [Member] | Accruing loans 90 days or more past due | Residential Mortgage [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value - Assets	570	552
Aggregate Unpaid Principal Balance - Assets	573	626
Difference - Assets	(3)	(74)
Loans - Portfolio [Member] | Nonaccrual Loans [Member] | Residential Mortgage [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value - Assets	270	365
Aggregate Unpaid Principal Balance - Assets	449	598
Difference - Assets	(179)	(233)
Loans - Portfolio [Member] | Quantifying Misstatement In Financial Statments - End of Period Impact | Residential Mortgage [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value - Assets		125
Aggregate Unpaid Principal Balance - Assets		128
Other Borrowed Funds [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value - Liabilities	273	309
Aggregate Unpaid Principal Balance - Liabilities	312	353
Difference - Liabilities	(39)	(44)
Other Borrowed Funds [Member] | Quantifying Misstatement In Financial Statments - End of Period Impact
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value - Liabilities		125
Aggregate Unpaid Principal Balance - Liabilities		$ 128