Segment Information - Additional Information (Detail) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013 Segment	Sep. 30, 2012
Segment Reporting Information [Line Items]
Number of reportable segments			3
Member co-share amounts and government subsidies	$ 1,300,000,000	$ 1,200,000,000	$ 3,900,000,000	$ 3,500,000,000
Depreciation and amortization classified as benefit expense	$ 23,000,000	$ 3,000,000	$ 69,000,000	$ 20,000,000