Risk Management (Narrative) (Details) (USD $)	Jun. 30, 2012 position	Dec. 31, 2011 position
Derivative [Line Items]
Notional amount of foreign currency derivatives	$ 360,000,000	$ 524,000,000
Number of net notional positions to buy or sell foreign currency disclosed (in number of positions)	5	5
Principal amount outstanding	1,900,000,000
Fair value of derivative liabilities	7,000,000	8,000,000
Aggregate credit risk with all counterparties	1,000,000
Not Designated As Hedging Instruments [Member]
Derivative [Line Items]
Fair value of derivative liabilities	6,000,000	6,000,000
Not Designated As Hedging Instruments [Member] | Interest Rate Contracts [Member] | Other Liabilities [Member]
Derivative [Line Items]
Fair value of derivative liabilities	$ 4,000,000	$ 3,000,000