Basis of Presentation - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended			12 Months Ended	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2014 Health Care Reform Program	Dec. 31, 2013 Health Care Reform	Mar. 31, 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			$ 548
Operating cost expense associated with amortization of deferred cost			137
Deferred cost asset			411	0
Percentage of premiums and services revenue applicable to risk spreading programs					16.00%
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			18
Ceded premiums			10	0
Ceded benefits			18	0
Payments due to HHS under risk adjustment, remittance period			30 days
Proceed for health care cost sharing subsidies for low-income individual members	$ 1,900	$ 1,500	$ 4