Fair Value (Fair Value Option for Certain Assets and Liabilities) (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Fair Value, Option, Quantitative Disclosures [Line Items]
Carrying value at estimated fair value	$ 225	$ 414
Carrying value at estimated fair value	57,508	56,592
Carrying value at estimated fair value	18,252	19,062
Consolidated Securitization Entities [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Unpaid principal balance	2,020	2,539
Difference between estimated fair value and unpaid principal balance	76	127
Carrying value at estimated fair value	2,096	2,666
Loans in non-accrual status	0	0
Loans more than 90 days past due	0	0
Loans in non-accrual status or more than 90 days past due, or both - difference between aggregate estimated fair value and unpaid principal balance	0	0
Contractual principal balance	1,918	2,430
Difference between estimated fair value and contractual principal balance	28	97
Carrying value at estimated fair value	1,946	2,527
Residential Mortgage Loans - FVO [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Unpaid principal balance	325	0
Difference between estimated fair value and unpaid principal balance	(113)	0
Carrying value at estimated fair value	212	0
Loans in non-accrual status	0	0
Loans more than 90 days past due	0	0
Loans in non-accrual status or more than 90 days past due, or both - difference between aggregate estimated fair value and unpaid principal balance	0	0
Mortgage Loans Held-for-sale [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Unpaid principal balance	0	80
Difference between estimated fair value and unpaid principal balance	0	(31)
Carrying value at estimated fair value	0	49
Loans in non-accrual status	0	3
Loans more than 90 days past due	0	23
Loans in non-accrual status or more than 90 days past due, or both - difference between aggregate estimated fair value and unpaid principal balance	$ 0	$ (14)