Investments - Scheduled maturities of available for sale fixed maturities (Details) $ in Millions	6 Months Ended
	Jun. 30, 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	$ 994
After one year through five years	7,703
After five years through ten years	13,386
After ten years	4,828
Fixed maturities amortized cost, Subtotal	26,911
ABS (average life of approximately 4-1/2 years)	8,849
MBS (average life of approximately 4-1/2 years)	3,484
Amortized Cost	39,244
Fair Value, Fiscal Year Maturity [Abstract]
One year or less	1,003
After one year through five years	7,764
After five years through ten years	13,285
After ten years	4,841
Fixed maturities fair value, Subtotal	26,893
ABS (average life of approximately 4-1/2 years)	8,935
MBS (average life of approximately 4-1/2 years)	3,820
Fair Value	$ 39,648
Fair Value Percent, Fiscal Year Maturity [Abstract]
One year or less	3.00%
After one year through five years	20.00%
After five years through ten years	33.00%
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%