Derivative Financial Instruments (Narrative) (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Derivative [Line Items]
Cash Collateral Received For Derivative Instruments	$ 1,680,000,000	$ 1,150,000,000
Cash Collateral Provided For Derivative Instruments	1,300,000,000	1,480,000,000
Weighted average life of trusts (in years)	6 years 11 months 5 days	7 years 4 months 24 days
Derivative Liability, Fair Value	495,000,000
Collateral already posted, aggregate fair value	14,000,000
Maximum additional amount of payments related to termination events	$ 481,000,000
Fair Value Hedges
Derivative [Line Items]
Securities Weighted Average Life, Years		7 years 4 months 24 days
Subordinated note matures	2018
Fair Value Hedges | 2.875% Senior Note [Member]
Derivative [Line Items]
Fixed interest rate	2.875%
Fair Value Hedges | 4.375% Senior Note [Member]
Derivative [Line Items]
Fixed interest rate	4.375%
Fair Value Hedges | 4.956% Subordinated Note [Member]
Derivative [Line Items]
Fixed interest rate	4.956%
Fair Value Hedges | 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	1 year 9 months 18 days	2 years 9 months 18 days