Investments - Scheduled maturities of available for sale fixed maturities (Details) $ in Millions	6 Months Ended
	Jun. 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	$ 1,029
After one year through five years	6,297
After five years through ten years	12,910
After ten years	4,596
Fixed maturities amortized cost, Subtotal	24,832
ABS (average life of approximately 5 years)	7,107
MBS (average life of approximately 4-1/2 years)	4,292
Amortized Cost	36,231
Fair Value, Fiscal Year Maturity [Abstract]
One year or less	1,041
After one year through five years	6,565
After five years through ten years	13,305
After ten years	4,754
Fixed maturities fair value, Subtotal	25,665
ABS (average life of approximately 5 years)	7,190
MBS (average life of approximately 4-1/2 years)	4,649
Fair Value	$ 37,504
Fair Value Percent, Fiscal Year Maturity [Abstract]
One year or less	3.00%
After one year through five years	18.00%
After five years through ten years	35.00%
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%