Investments - Investments - Mortgage Loans by Region and Property Type (Details) - USD ($) $ in Millions	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, before Allowance for Credit Loss			$ 4,215
Financing Receivable, Allowance for Credit Loss			0
Commercial Loan [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, before Allowance for Credit Loss	$ 4,442		$ 4,215
Percent of Total	100.00%		100.00%
Financing Receivable, Allowance for Credit Loss	$ 43	$ 21	$ 0	$ 0	$ 1	$ 1
Commercial Loan [Member] | Industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, before Allowance for Credit Loss	$ 1,298		$ 1,167
Percent of Total	29.20%		27.70%
Commercial Loan [Member] | Multifamily
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, before Allowance for Credit Loss	$ 1,427		$ 1,313
Percent of Total	32.10%		31.20%
Commercial Loan [Member] | Office
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, before Allowance for Credit Loss	$ 757		$ 723
Percent of Total	17.10%		17.20%
Commercial Loan [Member] | Retail
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, before Allowance for Credit Loss	$ 785		$ 735
Percent of Total	17.70%		17.40%
Commercial Loan [Member] | Residential Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, before Allowance for Credit Loss	$ 135		$ 137
Percent of Total	3.00%		3.20%
Commercial Loan [Member] | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, before Allowance for Credit Loss	$ 40		$ 140
Percent of Total	0.90%		3.30%
Commercial Loan [Member] | Mortgages [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percent of Total	100.00%		100.00%
Commercial Loan [Member] | East North Central [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, before Allowance for Credit Loss	$ 284		$ 270
Commercial Loan [Member] | East North Central [Member] | Mortgages [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percent of Total	6.40%		6.40%
Commercial Loan [Member] | Middle Atlantic [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, before Allowance for Credit Loss	$ 338		$ 319
Commercial Loan [Member] | Middle Atlantic [Member] | Mortgages [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percent of Total	7.60%		7.50%
Commercial Loan [Member] | Mountain [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, before Allowance for Credit Loss	$ 185		$ 109
Commercial Loan [Member] | Mountain [Member] | Mortgages [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percent of Total	4.20%		2.60%
Commercial Loan [Member] | New England [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, before Allowance for Credit Loss	$ 398		$ 344
Commercial Loan [Member] | New England [Member] | Mortgages [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percent of Total	9.00%		8.20%
Commercial Loan [Member] | Pacific [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, before Allowance for Credit Loss	$ 931		$ 906
Commercial Loan [Member] | Pacific [Member] | Mortgages [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percent of Total	20.90%		21.50%
Commercial Loan [Member] | South Atlantic [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, before Allowance for Credit Loss	$ 955		$ 944
Commercial Loan [Member] | South Atlantic [Member] | Mortgages [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percent of Total	21.50%		22.40%
Commercial Loan [Member] | West North Central [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, before Allowance for Credit Loss	$ 44		$ 46
Commercial Loan [Member] | West North Central [Member] | Mortgages [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percent of Total	1.00%		1.10%
Commercial Loan [Member] | West South Central [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, before Allowance for Credit Loss	$ 475		$ 439
Commercial Loan [Member] | West South Central [Member] | Mortgages [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percent of Total	10.70%		10.40%
Commercial Loan [Member] | Region Others [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, before Allowance for Credit Loss	$ 832		$ 838
Commercial Loan [Member] | Region Others [Member] | Mortgages [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percent of Total	18.70%		19.90%