Non-recurring Fair Value Measurements (Details 3) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Non-Recurring Fair Value Measurements
Fair value on a non-recurring basis of financial investments	$ 0	$ 2
Impairment charges for financial investments	(17)	(34)	(10)
Private Equity Funds [Member]
Non-Recurring Fair Value Measurements
Fair value on a non-recurring basis of financial investments	0	2
Other private investments [Member]
Non-Recurring Fair Value Measurements
Impairment charges for financial investments	0	0
Quoted Market Prices (Level 1) [Member]
Non-Recurring Fair Value Measurements
Fair value on a non-recurring basis of financial investments	0	0
Quoted Market Prices (Level 1) [Member] | Private Equity Funds [Member]
Non-Recurring Fair Value Measurements
Fair value on a non-recurring basis of financial investments	0	0
Quoted Market Prices (Level 1) [Member] | Other private investments [Member]
Non-Recurring Fair Value Measurements
Impairment charges for financial investments	0	0
Significant Other Observable Inputs (Level 2) [Member]
Non-Recurring Fair Value Measurements
Fair value on a non-recurring basis of financial investments	0	0
Significant Other Observable Inputs (Level 2) [Member] | Private Equity Funds [Member]
Non-Recurring Fair Value Measurements
Fair value on a non-recurring basis of financial investments	0	0
Significant Other Observable Inputs (Level 2) [Member] | Other private investments [Member]
Non-Recurring Fair Value Measurements
Impairment charges for financial investments	0	0
Significant Unobservable Inputs (Level 3) [Member]
Non-Recurring Fair Value Measurements
Fair value on a non-recurring basis of financial investments	0	2
Significant Unobservable Inputs (Level 3) [Member] | Private Equity Funds [Member]
Non-Recurring Fair Value Measurements
Fair value on a non-recurring basis of financial investments	0	2
Significant Unobservable Inputs (Level 3) [Member] | Other private investments [Member]
Non-Recurring Fair Value Measurements
Impairment charges for financial investments	0	0
Total Gains (Losses) [Member]
Non-Recurring Fair Value Measurements
Fair value on a non-recurring basis of financial investments	0	(6)
Total Gains (Losses) [Member] | Private Equity Funds [Member]
Non-Recurring Fair Value Measurements
Fair value on a non-recurring basis of financial investments	0	(4)
Total Gains (Losses) [Member] | Other private investments [Member]
Non-Recurring Fair Value Measurements
Impairment charges for financial investments	$ 0	$ (2)