Fair Value (Fair Value Option for Certain Assets and Liabilities) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Fair Value, Option, Quantitative Disclosures [Line Items]
Carrying value at estimated fair value	$ 2	$ 49
Carrying value at estimated fair value	55,343	56,592
Residential Mortgage Loans Held For Sale [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Unpaid principal balance	4	80
Difference between estimated fair value and unpaid principal balance	(2)	(31)
Carrying value at estimated fair value	2	49
Loans in non-accrual status	1	3
Loans more than 90 days past due	1	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	(2)	(14)
Assets and Liabilities Held by CSEs [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Unpaid principal balance	2,293	2,539
Difference between estimated fair value and unpaid principal balance	114	127
Carrying value at estimated fair value	2,407	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	2,191	2,430
Difference between estimated fair value and contractual principal balance	77	97
Carrying value at estimated fair value	$ 2,268	$ 2,527