Derivative Financial Instruments (Narrative) (Details) (USD $)	6 Months Ended		12 Months Ended
	Jun. 30, 2013		Dec. 31, 2012
Derivative [Line Items]
Cash collateral received for derivative instruments	$ 1,260,000,000		$ 1,680,000,000
Cash collateral provided for derivative instruments	3,250,000,000		1,300,000,000
Fair value of derivative liabilities	11,534,000,000	[1]	9,438,000,000	[1]
Weighted average life of trusts (in years)	6 years 9 months 18 days		6 years 11 months
Credit swap agreements
Derivative [Line Items]
Fair value of derivative liabilities	1,060,000,000
Collateral already posted, aggregate fair value	65,000,000
Maximum additional amount of payments related to termination events	$ 991,000,000
Fair Value Hedges | Interest rate swap | Senior notes
Derivative [Line Items]
Number of securities	2
Fair Value Hedges | Interest rate swap | Subordinated note
Derivative [Line Items]
Number of securities	1
Fair Value Hedges | 4.375% Senior Note | Interest rate swap
Derivative [Line Items]
Fixed interest rate	4.375%
Fair Value Hedges | 1.35% Senior Note
Derivative [Line Items]
Fixed interest rate	1.35%
Fair Value Hedges | 1.35% Senior Note | Interest rate swap | Subordinated note
Derivative [Line Items]
Number of securities	1
Fair Value Hedges | 3.1% Subordinated Note | Interest rate swap
Derivative [Line Items]
Fixed interest rate	3.10%
Cash Flow Hedges
Derivative [Line Items]
Securities weighted average life (in years)	1 year 3 months 18 days		1 year 9 months 18 days

[1] Amounts include all transactions regardless of whether or not they are subject to an enforceable netting arrangement.