Investments - Scheduled maturities of available for sale fixed maturities (Details) - Fixed maturities $ in Millions	Sep. 30, 2016 USD ($)
Amortized Cost Basis, Fiscal Year Maturity [Abstract]
One year or less	$ 1,036
After one year through five years	5,686
After five years through ten years	11,767
After ten years	3,959
Fixed maturities amortized cost, Subtotal	22,448
ABS (average life of approximately 5 years)	5,844
MBS (average life of approximately 4 years)	5,294
Amortized Cost	33,586
Fair Value, Fiscal Year Maturity [Abstract]
One year or less	1,053
After one year through five years	6,047
After five years through ten years	12,467
After ten years	4,273
Fixed maturities fair value, Subtotal	23,840
ABS (average life of approximately 5 years)	5,889
MBS (average life of approximately 4 years)	5,665
Fair Value	$ 35,394
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	12.00%
Fixed maturities fair value, Subtotal, Percent	67.00%
ABS (average life of approximately 5 years)	17.00%
MBS (average life of approximately 4 years)	16.00%
Fair value, Total, Percent	100.00%