Investments - Scheduled maturities of available for sale fixed maturities (Details) - Fixed maturities $ in Millions	Dec. 31, 2016 USD ($)
Amortized Cost Basis, Fiscal Year Maturity [Abstract]
One year or less	$ 1,120
After one year through five years	5,609
After five years through ten years	11,744
After ten years	4,487
Fixed maturities amortized cost, Subtotal	22,960
ABS (average life of approximately 5 years)	5,962
MBS (average life of approximately 4.5 years)	4,813
Amortized Cost	33,735
Fair Value, Fiscal Year Maturity [Abstract]
One year or less	1,136
After one year through five years	5,866
After five years through ten years	11,921
After ten years	4,534
Fixed maturities fair value, Subtotal	23,457
ABS (average life of approximately 5 years)	5,959
MBS (average life of approximately 4.5 years)	5,128
Fair Value	$ 34,544
Fair Value Percent, Fiscal Year Maturity [Abstract]
One year or less	3.00%
After one year through five years	17.00%
After five years through ten years	35.00%
After ten years	13.00%
Fixed maturities fair value, Subtotal, Percent	68.00%
ABS (average life of approximately 5 years)	17.00%
MBS (average life of approximately 4.5 years)	15.00%
Fair value, Total, Percent	100.00%