Risk Adjustment, Risk Corridor and Reinsurance Recoverable Settlements (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Effects of Risk Spreading Premium Stabilization Programs [Line Items]
Trade accounts payable and accrued expenses	$ (2,559)	$ (1,821)
Other long-term assets	2,155	1,774
Other long-term liabilities	(360)	(289)
Risk Adjustment/Risk Corridor Settlement [Member] | Health Care Reform
Effects of Risk Spreading Premium Stabilization Programs [Line Items]
Other long-term assets	102
Other long-term liabilities	(15)
Net long-term asset	87
Total net asset (liability)	87
Reinsurance Contribution | Health Care Reform
Effects of Risk Spreading Premium Stabilization Programs [Line Items]
Trade accounts payable and accrued expenses	(63)
Total net asset (liability)	(63)
Reinsurance Recoverable | Health Care Reform
Effects of Risk Spreading Premium Stabilization Programs [Line Items]
Other long-term assets	153
Net long-term asset	153
Total net asset (liability)	$ 153