Fair Value Measurements (Narrative) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010
Fair Value Measurement [Line Items]
Percentage of unadjusted fair values obtained	98.00%
Percentage of specific unadjusted broker quotes obtained	2.00%
Transfers between Levels 1, 2, and 3 of the fair value hierarchy	$ 0	$ 0
Changes in financial assets related to liquidity assumptions	$ 10	$ 0
Minimum [Member]
Fair Value Measurement [Line Items]
Number of knowledgeable outside security brokers consulted to determine fair value	1