Investments - Loans by Loan to Value (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Schedule of Loans by Loan to Value Ratio [Line Items]
Benchmark loan to value ratio, greater than indicates unpaid loan amount exceeds underlying collateral	100.00%
Total Commercial mortgage loans	$ 4,919	$ 4,911
Range One
Schedule of Loans by Loan to Value Ratio [Line Items]
Loan to Value Ratio, minimum	0.00%	0.00%
Loan to Value Ratio, maximum	50.00%	50.00%
Range Two
Schedule of Loans by Loan to Value Ratio [Line Items]
Loan to Value Ratio, minimum	50.00%	50.00%
Loan to Value Ratio, maximum	60.00%	60.00%
Range Three
Schedule of Loans by Loan to Value Ratio [Line Items]
Loan to Value Ratio, minimum	60.00%	60.00%
Loan to Value Ratio, maximum	70.00%	70.00%
Range Four
Schedule of Loans by Loan to Value Ratio [Line Items]
Loan to Value Ratio, minimum	70.00%	70.00%
Loan to Value Ratio, maximum	80.00%	80.00%
Range Five
Schedule of Loans by Loan to Value Ratio [Line Items]
Loan to Value Ratio, minimum	80.00%	80.00%