Fair Value (Fair Value Option - Fair Value and Principal Balances) (Details) - USD ($) $ in Millions	Jun. 30, 2015	Dec. 31, 2014
Customer Resale Agreements [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value - Assets	$ 150	$ 155
Aggregate Unpaid Principal Balance - Assets	143	148
Difference - Assets	7	7
Trading Loans [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value - Assets	48	37
Aggregate Unpaid Principal Balance - Assets	48	37
Loans Held For Sale [Member] | Residential Mortgage [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value - Assets	1,364	1,261
Aggregate Unpaid Principal Balance - Assets	1,328	1,202
Difference - Assets	36	59
Loans Held For Sale [Member] | Commercial Mortgage [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value - Assets	757	893
Aggregate Unpaid Principal Balance - Assets	771	972
Difference - Assets	(14)	(79)
Loans Held For Sale [Member] | Performing Loans [Member] | Residential Mortgage [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value - Assets	1,338	1,236
Aggregate Unpaid Principal Balance - Assets	1,300	1,176
Difference - Assets	38	60
Loans Held For Sale [Member] | Performing Loans [Member] | Commercial Mortgage [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value - Assets	755	873
Aggregate Unpaid Principal Balance - Assets	768	908
Difference - Assets	(13)	(35)
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	9
Aggregate Unpaid Principal Balance - Assets	3	9
Loans Held For Sale [Member] | Nonaccrual Loans [Member] | Residential Mortgage [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value - Assets	23	16
Aggregate Unpaid Principal Balance - Assets	25	17
Difference - Assets	(2)	(1)
Loans Held For Sale [Member] | Nonaccrual Loans [Member] | Commercial Mortgage [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value - Assets	2	20
Aggregate Unpaid Principal Balance - Assets	3	64
Difference - Assets	(1)	(44)
Loans - Portfolio [Member] | Residential Mortgage [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value - Assets	941	1,034
Aggregate Unpaid Principal Balance - Assets	1,157	1,278
Difference - Assets	(216)	(244)
Loans - Portfolio [Member] | Performing Loans [Member] | Residential Mortgage [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value - Assets	230	194
Aggregate Unpaid Principal Balance - Assets	289	256
Difference - Assets	(59)	(62)
Loans - Portfolio [Member] | Accruing loans 90 days or more past due | Residential Mortgage [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value - Assets	468	570
Aggregate Unpaid Principal Balance - Assets	471	573
Difference - Assets	(3)	(3)
Loans - Portfolio [Member] | Nonaccrual Loans [Member] | Residential Mortgage [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value - Assets	243	270
Aggregate Unpaid Principal Balance - Assets	397	449
Difference - Assets	(154)	(179)
Other Borrowed Funds [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value - Liabilities	224	273
Aggregate Unpaid Principal Balance - Liabilities	260	312
Difference - Liabilities	$ (36)	$ (39)