Investments - Scheduled maturities of available for sale fixed maturities (Details) $ in Millions	3 Months Ended
	Mar. 31, 2018 USD ($)
Fair Value Percent, Fiscal Year Maturity [Abstract]
Average life of ABS	4 years 6 months
Average life of MBS	4 years 6 months
Fixed maturities
Amortized Cost Basis, Fiscal Year Maturity [Abstract]
One year or less	$ 793
After one year through five years	7,314
After five years through ten years	13,345
After ten years	4,731
Fixed maturities amortized cost, Subtotal	26,183
ABS (average life of approximately 4-1/2 years)	8,546
MBS (average life of approximately 4-1/2 years)	3,654
Amortized Cost	38,383
Fair Value, Fiscal Year Maturity [Abstract]
One year or less	804
After one year through five years	7,431
After five years through ten years	13,425
After ten years	4,799
Fixed maturities fair value, Subtotal	26,459
ABS (average life of approximately 4-1/2 years)	8,663
MBS (average life of approximately 4-1/2 years)	4,003
Fair Value	$ 39,125
Fair Value Percent, Fiscal Year Maturity [Abstract]
One year or less	2.00%
After one year through five years	19.00%
After five years through ten years	35.00%
After ten years	12.00%
Fixed maturities fair value, Subtotal, Percent	68.00%
ABS (average life of approximately 4-1/2 years)	22.00%
MBS (average life of approximately 4-1/2 years)	10.00%
Fair value, Total, Percent	100.00%