Contingencies and Other Matters - Legal and Regulatory Matters (Details) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2017	Dec. 31, 2016
CMS Actions [Member]
Loss Contingencies [Line Items]
Charges for loss contingency, after-tax		$ 100
Percent of Medicare Advantage customers in a 4 Star or greater plan	60.00%
Guaranty Fund Assessments [Member]
Loss Contingencies [Line Items]
Charges for loss contingency, pre-tax	$ 130
Charges for loss contingency, after-tax	$ 85
Discount rate, Penn Treaty assessments	3.50%
Recorded liability, Penn Treaty assessment	$ 100
Total future expected cash outflows, Penn Treaty assessment	130
Pending Litigation [Member]
Loss Contingencies [Line Items]
Reserves for litigation matters, pre-tax	190
Reserves for litigation matters, after-tax	$ 125