Amounts Associated With 3Rs (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014	Dec. 31, 2015	Oct. 01, 2015
Supplementary Insurance Information, by Segment [Line Items]
Other current assets	$ 15,773		$ 15,773		$ 15,536
Trade accounts payable and accrued expenses	(2,216)		(2,216)		(2,095)
Other long-term assets	2,035		2,035		1,583
Other long-term liabilities	(225)		(225)		(236)
Risk Adjustment Settlement
Supplementary Insurance Information, by Segment [Line Items]
Total net (liability) asset	(49)		(49)		42
Reinsurance Recoverables
Supplementary Insurance Information, by Segment [Line Items]
Total net (liability) asset	411		411		586
Risk Corridor Settlement
Supplementary Insurance Information, by Segment [Line Items]
Total net (liability) asset	446		446		51
Health Care Reform
Supplementary Insurance Information, by Segment [Line Items]
Decline in the estimated net receivable			(43)
Payment of annual health insurance industry fee			867		562
Amortization of deferred charges	217	$ 141	650	$ 421
Deferred costs	217		217
2014 Coverage Year
Supplementary Insurance Information, by Segment [Line Items]
Risk adjustment charges	186
Proceeds from reinsurance recoverable	481
2014 Coverage Year | Risk Adjustment Settlement
Supplementary Insurance Information, by Segment [Line Items]
Proceeds from settlements	50
Premiums receivable	10		10		131
Other current assets	0		0		0
Trade accounts payable and accrued expenses	0		0		(89)
Net current asset	10		10		42
Other long-term assets	0		0		0
Other long-term liabilities	0		0		0
Net long-term asset	0		0		0
Total net (liability) asset	10		10		42
2014 Coverage Year | Reinsurance Recoverables
Supplementary Insurance Information, by Segment [Line Items]
Premiums receivable	0		0		0
Other current assets	40		40		586
Trade accounts payable and accrued expenses	0		0		0
Net current asset	40		40		586
Other long-term assets	0		0		0
Other long-term liabilities	0		0		0
Net long-term asset	0		0		0
Total net (liability) asset	40		40		586
2014 Coverage Year | Risk Corridor Settlement
Supplementary Insurance Information, by Segment [Line Items]
Insurance settlements receivable, current	31		31
Premiums receivable	0		0		0
Other current assets	31		31		55
Trade accounts payable and accrued expenses	(1)		(1)		(4)
Net current asset	30		30		51
Other long-term assets	211		211		0
Other long-term liabilities	0		0		0
Net long-term asset	211		211		0
Total net (liability) asset	241		241		51
2015 Coverage Year | Risk Adjustment Settlement
Supplementary Insurance Information, by Segment [Line Items]
Premiums receivable	88		88		0
Other current assets	0		0		0
Trade accounts payable and accrued expenses	(154)		(154)		0
Net current asset	(66)		(66)		0
Other long-term assets	7		7		0
Other long-term liabilities	0		0		0
Net long-term asset	7		7		0
Total net (liability) asset	(59)		(59)		0
2015 Coverage Year | Reinsurance Recoverables
Supplementary Insurance Information, by Segment [Line Items]
Premiums receivable	0		0		0
Other current assets	344		344		0
Trade accounts payable and accrued expenses	0		0		0
Net current asset	344		344		0
Other long-term assets	27		27		0
Other long-term liabilities	0		0		0
Net long-term asset	27		27		0
Total net (liability) asset	371		371		0
2015 Coverage Year | Risk Corridor Settlement
Supplementary Insurance Information, by Segment [Line Items]
Premiums receivable	0		0		0
Other current assets	0		0		0
Trade accounts payable and accrued expenses	(1)		(1)		0
Net current asset	(1)		(1)		0
Other long-term assets	206		206		0
Other long-term liabilities	0		0		0
Net long-term asset	206		206		0
Total net (liability) asset	$ 205		$ 205		$ 0
Scenario, Forecast | 2014 Coverage Year | Risk Adjustment Settlement
Supplementary Insurance Information, by Segment [Line Items]
Reinsurance recoverable and risk adjustment receivable, net						$ 50
Subsequent Event | 2014 Coverage Year | Risk Corridor Settlement
Supplementary Insurance Information, by Segment [Line Items]
Percent of receivable to be paid by CMS (between December 2015 and January 2016)							12.60%