Comprehensive income and accumulated other comprehensive loss (Details) (USD $) In Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010	Dec. 31, 2010
Comprehensive income and accumulated other comprehensive income (loss)
Net income	$ 148	$ 51	$ 986	$ 651
Other comprehensive income:
Foreign currency translation adjustment	(58)	48	(18)	15
Unrealized appreciation (depreciation) on investments, net of taxes	0	0	2	0
Other comprehensive income (loss)	(58)	48	(16)	15
Total comprehensive income	90	99	970	666
Accumulated other comprehensive income (loss).
Foreign currency translation adjustment	(29)		(29)		(11)
Unrealized depreciation on investments, net of deferred income taxes of $0 for September 30, 2011 and $(1) for December 31, 2010	0		0		(2)
Accumulated other comprehensive income (loss)	(29)		(29)		(13)
Deferred income taxes on gross unrealized appreciation (depreciation) on investments			$ 0		$ (1)