Basis of Presentation - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended			12 Months Ended	6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014 Health Care Reform Program	Dec. 31, 2013 Health Care Reform	Jun. 30, 2014 Commercial Medical
Organization, Consolidation and Presentation of Financial Statements Disclosure [Line Items]
Number of premium stabilization programs					3
Annual health insurance industry fee for calendar year 2014 to be paid in September 2014					$ 560
Operating cost expense associated with amortization of deferred cost					280
Deferred cost asset					280	0
Percentage of premiums and services revenue applicable to risk spreading programs							17.20%
Payment of risk adjustment audit by health and human services in 2014 or 2015, first two years of the program					0
Operating costs associated with transitional reinsurance contributions					50
Ceded premiums					13	0
Ceded benefits					153	0
Payments due to HHS under risk adjustment, remittance period					30 days
Proceed for health care cost sharing subsidies for low-income individual members	$ 2,300	$ 1,700	$ 4,100	$ 3,200	$ 24