Summary of Significant Accounting Policies - Significant Accounting Policies (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Accounting Policies [Abstract]
Allowance for doubtful accounts and unrecoverable reinsurance	$ 203	$ 78
Amortization for policy acquisition costs recorded primarily in other operating expense	$ 292	$ 286	$ 289
Percent of ASO fees at risk for performance guarantees	10.00%
Minimum [Member]
Future policy benefits interest rate assumptions	0.10%
Maximum [Member]
Future policy benefits interest rate assumptions	9.00%
Percent of ASO fees reimbursed for performance guarantees	1.00%