Investments - Scheduled maturities of available for sale fixed maturities (Details) $ in Millions	9 Months Ended
	Sep. 30, 2017 USD ($)
Fair Value Percent, Fiscal Year Maturity [Abstract]
Average life of ABS	5 years
Average life of MBS	4 years 6 months
Fixed maturities
Amortized Cost Basis, Fiscal Year Maturity [Abstract]
One year or less	$ 927
After one year through five years	6,521
After five years through ten years	13,074
After ten years	4,593
Fixed maturities amortized cost, Subtotal	25,115
ABS (average life of approximately 5 years)	7,268
MBS (average life of approximately 4-1/2 years)	4,029
Amortized Cost	36,412
Fair Value, Fiscal Year Maturity [Abstract]
One year or less	939
After one year through five years	6,787
After five years through ten years	13,527
After ten years	4,763
Fixed maturities fair value, Subtotal	26,016
ABS (average life of approximately 5 years)	7,396
MBS (average life of approximately 4-1/2 years)	4,406
Fair Value	$ 37,818
Fair Value Percent, Fiscal Year Maturity [Abstract]
One year or less	2.00%
After one year through five years	18.00%
After five years through ten years	36.00%
After ten years	13.00%
Fixed maturities fair value, Subtotal, Percent	69.00%
ABS (average life of approximately 5 years)	19.00%
MBS (average life of approximately 4-1/2 years)	12.00%
Fair value, Total, Percent	100.00%