Fair Value (Fair Value Option - Fair Value and Principal Balances) (Details) - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015
Customer Resale Agreements [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value - Assets	$ 138	$ 137
Aggregate Unpaid Principal Balance - Assets	134	133
Difference - Assets	4	4
Loans Held For Sale [Member] | Residential Mortgage [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value - Assets	780	843
Aggregate Unpaid Principal Balance - Assets	744	816
Difference - Assets	36	27
Loans Held For Sale [Member] | Commercial Mortgage [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value - Assets	655	641
Aggregate Unpaid Principal Balance - Assets	662	662
Difference - Assets	(7)	(21)
Loans Held For Sale [Member] | Performing Loans [Member] | Residential Mortgage [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value - Assets	767	832
Aggregate Unpaid Principal Balance - Assets	731	804
Difference - Assets	36	28
Loans Held For Sale [Member] | Performing Loans [Member] | Commercial Mortgage [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value - Assets	652	639
Aggregate Unpaid Principal Balance - Assets	657	659
Difference - Assets	(5)	(20)
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	4	4
Aggregate Unpaid Principal Balance - Assets	4	4
Loans Held For Sale [Member] | Nonaccrual Loans [Member] | Residential Mortgage [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value - Assets	9	7
Aggregate Unpaid Principal Balance - Assets	9	8
Difference - Assets		(1)
Loans Held For Sale [Member] | Nonaccrual Loans [Member] | Commercial Mortgage [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value - Assets	3	2
Aggregate Unpaid Principal Balance - Assets	5	3
Difference - Assets	(2)	(1)
Loans - Portfolio [Member] | Residential Mortgage [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value - Assets	895	905
Aggregate Unpaid Principal Balance - Assets	1,084	1,099
Difference - Assets	(189)	(194)
Loans - Portfolio [Member] | Performing Loans [Member] | Residential Mortgage [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value - Assets	270	204
Aggregate Unpaid Principal Balance - Assets	313	260
Difference - Assets	(43)	(56)
Loans - Portfolio [Member] | Accruing loans 90 days or more past due | Residential Mortgage [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value - Assets	410	475
Aggregate Unpaid Principal Balance - Assets	410	478
Difference - Assets		(3)
Loans - Portfolio [Member] | Nonaccrual Loans [Member] | Residential Mortgage [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value - Assets	215	226
Aggregate Unpaid Principal Balance - Assets	361	361
Difference - Assets	(146)	(135)
Other Assets [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value - Assets	167	164
Aggregate Unpaid Principal Balance - Assets	172	159
Difference - Assets	(5)	5
Other Borrowed Funds [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value - Liabilities	63	93
Aggregate Unpaid Principal Balance - Liabilities	64	95
Difference - Liabilities	$ (1)	$ (2)