Risk Adjustment, Risk Corridor and Reinsurance Recoverable Settlements (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Effects of Risk Spreading Premium Stabilization Programs [Line Items]
Trade accounts payable and accrued expenses	$ (2,752)	$ (1,821)
Other long-term assets	1,848	1,774
Other long-term liabilities	(330)	(289)
Risk Adjustment Settlement | Health Care Reform
Effects of Risk Spreading Premium Stabilization Programs [Line Items]
Trade accounts payable and accrued expenses	0
Other long-term assets	25
Other long-term liabilities	(2)
Net long-term asset	23
Total net asset (liability)	23
Risk Corridor Settlements | Health Care Reform
Effects of Risk Spreading Premium Stabilization Programs [Line Items]
Trade accounts payable and accrued expenses	0
Other long-term assets	16
Other long-term liabilities	(3)
Net long-term asset	13
Total net asset (liability)	13
Reinsurance Contribution | Health Care Reform
Effects of Risk Spreading Premium Stabilization Programs [Line Items]
Trade accounts payable and accrued expenses	(28)
Other long-term assets	0
Other long-term liabilities	0
Net long-term asset	0
Total net asset (liability)	(28)
Reinsurance Recoverable | Health Care Reform
Effects of Risk Spreading Premium Stabilization Programs [Line Items]
Trade accounts payable and accrued expenses	0
Other long-term assets	18
Other long-term liabilities	0
Net long-term asset	18
Total net asset (liability)	$ 18