Summary of Significant Accounting Policies - Additional Information (Detail) (USD $)	12 Months Ended	9 Months Ended	12 Months Ended
	Dec. 31, 2012 D Y	Dec. 31, 2012 New Tricare South Region Contract	Dec. 31, 2012 Equipment Minimum	Dec. 31, 2012 Equipment Maximum	Dec. 31, 2012 Computer Software Minimum	Dec. 31, 2012 Computer Software Maximum	Dec. 31, 2012 Building Minimum	Dec. 31, 2012 Building Maximum
Significant Accounting Policies [Line Items]
Typical term (in years) of short-duration employer-group prepaid health services policies	1
Number of days notice for employer group to cancel short-duration prepaid health services policies	30
Consumer discounts on brand name prescription drugs	50.00%
TRICARE Health care cost payments		$ 2,100,000,000
TRICARE Health care cost reimbursements		2,000,000,000
Difference between TRICARE health care costs payments and reimbursements		$ 56,000,000
Useful life			3 years	10 years	3 years	7 years	20 years	40 years