Investments - Mortgage Loans, Net by Property Type and Geographic Region (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Loans and Leases Receivable Disclosure [Line Items]
Mortgage loans, net of allowances	$ 15,203	$ 14,306
Commercial mortgage loans
Loans and Leases Receivable Disclosure [Line Items]
Mortgage loans, net of allowances	$ 11,231	$ 10,505
Commercial mortgage loans | Property Type Concentration Risk | Mortgage Loans, Net
Loans and Leases Receivable Disclosure [Line Items]
Percentage concentration risk	100.00%	100.00%
Commercial mortgage loans | Geographic Concentration Risk | Mortgage Loans, Net
Loans and Leases Receivable Disclosure [Line Items]
Percentage concentration risk	100.00%	100.00%
Commercial mortgage loans | Total U.S. Region
Loans and Leases Receivable Disclosure [Line Items]
Mortgage loans, net of allowances	$ 10,996	$ 10,271
Commercial mortgage loans | Total U.S. Region | Geographic Concentration Risk | Mortgage Loans, Net
Loans and Leases Receivable Disclosure [Line Items]
Percentage concentration risk	97.90%	97.80%
Commercial mortgage loans | East North Central
Loans and Leases Receivable Disclosure [Line Items]
Mortgage loans, net of allowances	$ 1,202	$ 1,036
Commercial mortgage loans | East North Central | Geographic Concentration Risk | Mortgage Loans, Net
Loans and Leases Receivable Disclosure [Line Items]
Percentage concentration risk	10.70%	9.90%
Commercial mortgage loans | East South Central
Loans and Leases Receivable Disclosure [Line Items]
Mortgage loans, net of allowances	$ 417	$ 428
Commercial mortgage loans | East South Central | Geographic Concentration Risk | Mortgage Loans, Net
Loans and Leases Receivable Disclosure [Line Items]
Percentage concentration risk	3.70%	4.10%
Commercial mortgage loans | Middle Atlantic
Loans and Leases Receivable Disclosure [Line Items]
Mortgage loans, net of allowances	$ 3,058	$ 2,580
Commercial mortgage loans | Middle Atlantic | Geographic Concentration Risk | Mortgage Loans, Net
Loans and Leases Receivable Disclosure [Line Items]
Percentage concentration risk	27.30%	24.60%
Commercial mortgage loans | Mountain
Loans and Leases Receivable Disclosure [Line Items]
Mortgage loans, net of allowances	$ 508	$ 528
Commercial mortgage loans | Mountain | Geographic Concentration Risk | Mortgage Loans, Net
Loans and Leases Receivable Disclosure [Line Items]
Percentage concentration risk	4.50%	5.00%
Commercial mortgage loans | New England
Loans and Leases Receivable Disclosure [Line Items]
Mortgage loans, net of allowances	$ 336	$ 340
Commercial mortgage loans | New England | Geographic Concentration Risk | Mortgage Loans, Net
Loans and Leases Receivable Disclosure [Line Items]
Percentage concentration risk	3.00%	3.20%
Commercial mortgage loans | Pacific
Loans and Leases Receivable Disclosure [Line Items]
Mortgage loans, net of allowances	$ 2,585	$ 2,502
Commercial mortgage loans | Pacific | Geographic Concentration Risk | Mortgage Loans, Net
Loans and Leases Receivable Disclosure [Line Items]
Percentage concentration risk	23.00%	23.80%
Commercial mortgage loans | South Atlantic
Loans and Leases Receivable Disclosure [Line Items]
Mortgage loans, net of allowances	$ 1,988	$ 1,920
Commercial mortgage loans | South Atlantic | Geographic Concentration Risk | Mortgage Loans, Net
Loans and Leases Receivable Disclosure [Line Items]
Percentage concentration risk	17.70%	18.30%
Commercial mortgage loans | West North Central
Loans and Leases Receivable Disclosure [Line Items]
Mortgage loans, net of allowances	$ 137	$ 146
Commercial mortgage loans | West North Central | Geographic Concentration Risk | Mortgage Loans, Net
Loans and Leases Receivable Disclosure [Line Items]
Percentage concentration risk	1.20%	1.40%
Commercial mortgage loans | West South Central
Loans and Leases Receivable Disclosure [Line Items]
Mortgage loans, net of allowances	$ 765	$ 791
Commercial mortgage loans | West South Central | Geographic Concentration Risk | Mortgage Loans, Net
Loans and Leases Receivable Disclosure [Line Items]
Percentage concentration risk	6.80%	7.50%
Commercial mortgage loans | Non-US [Member]
Loans and Leases Receivable Disclosure [Line Items]
Mortgage loans, net of allowances	$ 235	$ 234
Commercial mortgage loans | Non-US [Member] | Geographic Concentration Risk | Mortgage Loans, Net
Loans and Leases Receivable Disclosure [Line Items]
Percentage concentration risk	2.10%	2.20%
Commercial mortgage loans | Hotels
Loans and Leases Receivable Disclosure [Line Items]
Mortgage loans, net of allowances	$ 1,131	$ 1,104
Commercial mortgage loans | Hotels | Property Type Concentration Risk | Mortgage Loans, Net
Loans and Leases Receivable Disclosure [Line Items]
Percentage concentration risk	10.10%	10.50%
Commercial mortgage loans | Retail
Loans and Leases Receivable Disclosure [Line Items]
Mortgage loans, net of allowances	$ 2,080	$ 2,182
Commercial mortgage loans | Retail | Property Type Concentration Risk | Mortgage Loans, Net
Loans and Leases Receivable Disclosure [Line Items]
Percentage concentration risk	18.50%	20.80%
Commercial mortgage loans | Office building
Loans and Leases Receivable Disclosure [Line Items]
Mortgage loans, net of allowances	$ 3,545	$ 2,899
Commercial mortgage loans | Office building | Property Type Concentration Risk | Mortgage Loans, Net
Loans and Leases Receivable Disclosure [Line Items]
Percentage concentration risk	31.60%	27.60%
Commercial mortgage loans | Industrial
Loans and Leases Receivable Disclosure [Line Items]
Mortgage loans, net of allowances	$ 1,385	$ 1,448
Commercial mortgage loans | Industrial | Property Type Concentration Risk | Mortgage Loans, Net
Loans and Leases Receivable Disclosure [Line Items]
Percentage concentration risk	12.30%	13.80%
Commercial mortgage loans | Apartment
Loans and Leases Receivable Disclosure [Line Items]
Mortgage loans, net of allowances	$ 2,401	$ 2,142
Commercial mortgage loans | Apartment | Property Type Concentration Risk | Mortgage Loans, Net
Loans and Leases Receivable Disclosure [Line Items]
Percentage concentration risk	21.40%	20.40%
Commercial mortgage loans | Other commercial
Loans and Leases Receivable Disclosure [Line Items]
Mortgage loans, net of allowances	$ 689	$ 730
Commercial mortgage loans | Other commercial | Property Type Concentration Risk | Mortgage Loans, Net
Loans and Leases Receivable Disclosure [Line Items]
Percentage concentration risk	6.10%	6.90%