Guarantees and Contingencies - Additional Information (Detail)	9 Months Ended
	Sep. 30, 2015 region
New Tricare South Region Contract
Loss Contingencies [Line Items]
Contract term, years	5 years
Contract expiration date	Mar. 31, 2017
Total Medicare
Loss Contingencies [Line Items]
Percentage of premiums and services revenue	72.00%
Military services
Loss Contingencies [Line Items]
Percentage of premiums and services revenue	1.00%
Number of regions	3
Number of regions after proposed consolidation	2
Medicaid
Loss Contingencies [Line Items]
Percentage of premiums and services revenue	4.00%