Guarantees and Contingencies - Additional Information (Detail)	9 Months Ended
	Sep. 30, 2013
Loss Contingencies [Line Items]
Period for filing notice of appeal	30 days
New Tricare South Region Contract
Loss Contingencies [Line Items]
Contract term, years	5 years
Contract expiration date	Mar. 31, 2017
Puerto Rico Health Insurance Administration Contracts East Southeast And Southwest Regions
Loss Contingencies [Line Items]
Contract term, years	3 years
Contract expiration date	Sep. 30, 2013
Medicare
Loss Contingencies [Line Items]
Percentage of premiums and services revenue	74.00%
Military Services
Loss Contingencies [Line Items]
Percentage of premiums and services revenue	1.00%
Medicaid
Loss Contingencies [Line Items]
Percentage of premiums and services revenue	3.00%