Segment Information - Additional Information (Detail) (USD $)	3 Months Ended			12 Months Ended
	Dec. 31, 2012	Jun. 30, 2012	Dec. 31, 2010	Dec. 31, 2012 Segment	Dec. 31, 2011	Dec. 31, 2010
Segment Reporting Information [Line Items]
Number of reportable segments				3
Member co-share amounts and government subsidies				$ 4,700,000,000	$ 4,200,000,000	$ 3,500,000,000
Depreciation and amortization classified as benefit expense				43,000,000	33,000,000	18,000,000
Percentage of total premium and services revenues derived from contracts with the federal government				75.00%	76.00%	76.00%
Litigation settlement associated with Military services business		46,000,000
Write-down of deferred acquisition costs						147,000,000
Charge related to closed block of long-term care policies	29,000,000		139,000,000	29,000,000		139,000,000
Other Businesses
Segment Reporting Information [Line Items]
Litigation settlement associated with Military services business				46,000,000
Charge related to closed block of long-term care policies						139,000,000
Retail
Segment Reporting Information [Line Items]
Write-down of deferred acquisition costs						$ 147,000,000