Derivative Financial Instruments (Narrative) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010
Derivative [Line Items]
Cash collateral received for derivative instruments	1,150	79
Cash collateral provided for derivative instruments	1,480	530
Derivative liability, fair value	911
Collateral already posted, aggregate fair value	276
Maximum additional amount of payments related to termination events	635.0
Fair Value Hedges [Member]
Derivative [Line Items]
Securities weighted-average life, years	7.4	7.7
Subordinated note matures	2018
Fair Value Hedges [Member] | 2.875% Senior Note [Member]
Derivative [Line Items]
Senior notes due	2016
Fixed interest rate	2.875%
Fair Value Hedges [Member] | 4.375% Senior Note [Member]
Derivative [Line Items]
Senior notes due	2021
Fixed interest rate	4.375%
Fair Value Hedges [Member] | 4.956% Subordinated Note [Member]
Derivative [Line Items]
Fixed interest rate	4.956%
Fair Value Hedges [Member] | 5.25% Subordinated Note [Member]
Derivative [Line Items]
Fixed interest rate	5.25%
Cash Flow Hedges [Member]
Derivative [Line Items]
Securities weighted-average life, years	2.8	3.8