Derivative Financial Instruments (Narrative) (Details) (USD $)	9 Months Ended	12 Months Ended
	Sep. 30, 2012	Dec. 31, 2011
Derivative [Line Items]
Cash Collateral Received For Derivative Instruments	1,150,000,000
Cash Collateral Provided For Derivative Instruments	1,170,000,000	1,480,000,000
Derivative Liability, Fair Value	641,000,000
Collateral already posted, aggregate fair value	188,000,000
Maximum additional amount of payments related to termination events	453,000,000
Fair Value Hedges [Member]
Derivative [Line Items]
Securities Weighted Average Life, Years	7 years 1 month 6 days	7 years 4 months 24 days
Subordinated note matures	2018
Fair Value Hedges [Member] | 2.875% Senior Note [Member]
Derivative [Line Items]
Fixed interest rate	2.875%
Fair Value Hedges [Member] | 4.375% Senior Note [Member]
Derivative [Line Items]
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 years	2 years 9 months 18 days