Investments, Amortized Cost Basis of Mortgage Loans for Each Credit Quality Indicator by Year of Origination (Details) - Mortgage Loans [Member] $ in Millions	Sep. 30, 2021 USD ($)	[1]
Mortgage Loans Amortized Cost Basis by Origination Year [Abstract]
2021	$ 63
2020	161
2019	282
2018	86
2017	169
Prior	296
Total	1,057
DSCR Greater than or Equal to 1.6x, LTV Less than 55% [Member]
Mortgage Loans Amortized Cost Basis by Origination Year [Abstract]
2021	8
2020	75
2019	16
2018	37
2017	116
Prior	203
Total	455
DSCR Greater than or Equal to 1.6x, LTV 55% to 65% [Member]
Mortgage Loans Amortized Cost Basis by Origination Year [Abstract]
2020	38
2019	15
2018	18
Prior	1
Total	72
DSCR Greater than or Equal to 1.6x, LTV Greater than 65% [Member]
Mortgage Loans Amortized Cost Basis by Origination Year [Abstract]
2021	17
2019	14
2018	7
Prior	23
Total	61
DSCR Between 1.2 to 1.6x, LTV Less than 55% [Member]
Mortgage Loans Amortized Cost Basis by Origination Year [Abstract]
2021	13
2020	15
2019	95
2017	5
Prior	58
Total	186
DSCR Between 1.2 to 1.6x, LTV 55% to 65% [Member]
Mortgage Loans Amortized Cost Basis by Origination Year [Abstract]
2021	25
2018	24
2017	10
Prior	4
Total	63
DSCR Between 1.2 to 1.6x, LTV Greater than 65% [Member]
Mortgage Loans Amortized Cost Basis by Origination Year [Abstract]
2020	24
2019	9
2017	8
Total	41
DSCR Less than or Equal to 1.2x, LTV Less than 55% [Member]
Mortgage Loans Amortized Cost Basis by Origination Year [Abstract]
2019	35
2017	30
Total	65
DSCR Less than or Equal to 1.2x, LTV 55% to 65% [Member]
Mortgage Loans Amortized Cost Basis by Origination Year [Abstract]
2019	42
Total	42
DSCR Less than or Equal to 1.2x, LTV Greater than 65% [Member]
Mortgage Loans Amortized Cost Basis by Origination Year [Abstract]
2020	9
2019	56
Prior	7
Total	$ 72

[1] The values in the table above reflect DSCR on a standardized amortization period and LTV ratios based on the most recent appraised values trended forward using changes in a commercial real estate price index.