Segment Information - Additional Information (Detail) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013 Segment	Jun. 30, 2012
Segment Reporting Information [Line Items]
Number of reportable segments			3
Member co-share amounts and government subsidies	$ 1,200,000,000	$ 1,200,000,000	$ 2,500,000,000	$ 2,400,000,000
Depreciation and amortization classified as benefit expense	$ 24,000,000	$ 9,000,000	$ 46,000,000	$ 17,000,000