Fair Value (Fair Value Option - Fair Value and Principal Balances) (Details) - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015
Customer Resale Agreements [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value - Assets	$ 137	$ 137
Aggregate Unpaid Principal Balance - Assets	133	133
Difference - Assets	4	4
Loans Held For Sale [Member] | Residential Mortgage [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value - Assets	1,116	843
Aggregate Unpaid Principal Balance - Assets	1,064	816
Difference - Assets	52	27
Loans Held For Sale [Member] | Commercial Mortgage [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value - Assets	981	641
Aggregate Unpaid Principal Balance - Assets	985	662
Difference - Assets	(4)	(21)
Loans Held For Sale [Member] | Performing Loans [Member] | Residential Mortgage [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value - Assets	1,104	832
Aggregate Unpaid Principal Balance - Assets	1,052	804
Difference - Assets	52	28
Loans Held For Sale [Member] | Performing Loans [Member] | Commercial Mortgage [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value - Assets	978	639
Aggregate Unpaid Principal Balance - Assets	980	659
Difference - Assets	(2)	(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	3	4
Aggregate Unpaid Principal Balance - Assets	3	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	851	905
Aggregate Unpaid Principal Balance - Assets	1,033	1,099
Difference - Assets	(182)	(194)
Loans - Portfolio [Member] | Performing Loans [Member] | Residential Mortgage [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value - Assets	234	204
Aggregate Unpaid Principal Balance - Assets	282	260
Difference - Assets	(48)	(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	402	475
Aggregate Unpaid Principal Balance - Assets	402	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	349	361
Difference - Assets	(134)	(135)
Other Assets [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value - Assets	140	164
Aggregate Unpaid Principal Balance - Assets	148	159
Difference - Assets	(8)	5
Other Borrowed Funds [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value - Liabilities	70	93
Aggregate Unpaid Principal Balance - Liabilities	71	95
Difference - Liabilities	$ (1)	$ (2)