Contingencies and Other Matters - Legal and Regulatory Matters (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Contingencies And Other Matters [Abstract]
Termination fee payable to Company	$ 1,850
CMS Actions [Member]
Loss Contingencies [Line Items]
Percent of Medicare Advantage customers in a 4 Star or greater plan	20.00%
Guaranty Fund Assessments [Member]
Loss Contingencies [Line Items]
Charges related to guaranty fund assessments
Company's share of guaranty fund assessment, after-tax	85
Pending Litigation [Member]
Loss Contingencies [Line Items]
Reserves for litigation matters, pre-tax	190
Reserves for litigation matters, after-tax	$ 125