Guaranteed Benefit Features - Universal and Variable Life Contracts (Details) - Variable Life and Universal Life - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Secondary Guarantees
Net Amount at Risk by Product and Guarantee [Line Items]
Account value (general and separate account)	$ 3,234	$ 3,262
Net amount at risk, net of reinsurance	$ 16,485	$ 16,372
Weighted average attained age	64 years	63 years
Paid-up Guarantees
Net Amount at Risk by Product and Guarantee [Line Items]
Account value (general and separate account)	$ 0	$ 0
Net amount at risk, net of reinsurance	$ 0	$ 0
Weighted average attained age	0 years	0 years