Medical Costs and Medical Costs Payable Rollforward (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Medical costs payable, beginning of period	$ 11,575	$ 11,004	$ 9,799
Acquisitions	0	0	1,029
Current year	93,677	89,970	81,086
Prior years	(420)	(680)	(860)
Total reported medical costs	93,257	89,290	80,226
Payments for current year	(82,374)	(78,989)	(71,832)
Payments for prior year	(10,418)	(9,730)	(8,218)
Total claim payments	(92,792)	(88,719)	(80,050)
Medical costs payable, end of period	$ 12,040	$ 11,575	$ 11,004