Segment Information - Revenue by Geographical Area (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Revenues from External Customers and Long-Lived Assets [Line Items]
Premiums and fees, mail order pharmacy revenues and other revenues	$ 9,174	$ 8,374	$ 18,292	$ 16,551