Investments - Mortgage Loans, Net by Property Type and Geographic Region (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Loans and Leases Receivable Disclosure [Line Items]
Mortgage loans, net of allowances	$ 14,395	$ 14,306
Commercial mortgage loans
Loans and Leases Receivable Disclosure [Line Items]
Mortgage loans, net of allowances	$ 11,078	$ 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	$ 10,868	$ 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	98.10%	97.80%
Commercial mortgage loans | East North Central
Loans and Leases Receivable Disclosure [Line Items]
Mortgage loans, net of allowances	$ 1,200	$ 1,036
Commercial mortgage loans | East North Central | Geographic Concentration Risk | Mortgage Loans, Net
Loans and Leases Receivable Disclosure [Line Items]
Percentage concentration risk	10.80%	9.90%
Commercial mortgage loans | East South Central
Loans and Leases Receivable Disclosure [Line Items]
Mortgage loans, net of allowances	$ 422	$ 428
Commercial mortgage loans | East South Central | Geographic Concentration Risk | Mortgage Loans, Net
Loans and Leases Receivable Disclosure [Line Items]
Percentage concentration risk	3.80%	4.10%
Commercial mortgage loans | Middle Atlantic
Loans and Leases Receivable Disclosure [Line Items]
Mortgage loans, net of allowances	$ 2,953	$ 2,580
Commercial mortgage loans | Middle Atlantic | Geographic Concentration Risk | Mortgage Loans, Net
Loans and Leases Receivable Disclosure [Line Items]
Percentage concentration risk	26.60%	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	4.60%	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	$ 2,559	$ 2,502
Commercial mortgage loans | Pacific | Geographic Concentration Risk | Mortgage Loans, Net
Loans and Leases Receivable Disclosure [Line Items]
Percentage concentration risk	23.10%	23.80%
Commercial mortgage loans | South Atlantic
Loans and Leases Receivable Disclosure [Line Items]
Mortgage loans, net of allowances	$ 1,980	$ 1,920
Commercial mortgage loans | South Atlantic | Geographic Concentration Risk | Mortgage Loans, Net
Loans and Leases Receivable Disclosure [Line Items]
Percentage concentration risk	17.90%	18.30%
Commercial mortgage loans | West North Central
Loans and Leases Receivable Disclosure [Line Items]
Mortgage loans, net of allowances	$ 140	$ 146
Commercial mortgage loans | West North Central | Geographic Concentration Risk | Mortgage Loans, Net
Loans and Leases Receivable Disclosure [Line Items]
Percentage concentration risk	1.30%	1.40%
Commercial mortgage loans | West South Central
Loans and Leases Receivable Disclosure [Line Items]
Mortgage loans, net of allowances	$ 770	$ 791
Commercial mortgage loans | West South Central | Geographic Concentration Risk | Mortgage Loans, Net
Loans and Leases Receivable Disclosure [Line Items]
Percentage concentration risk	7.00%	7.50%
Commercial mortgage loans | Non-US [Member]
Loans and Leases Receivable Disclosure [Line Items]
Mortgage loans, net of allowances	$ 210	$ 234
Commercial mortgage loans | Non-US [Member] | Geographic Concentration Risk | Mortgage Loans, Net
Loans and Leases Receivable Disclosure [Line Items]
Percentage concentration risk	1.90%	2.20%
Commercial mortgage loans | Hotels
Loans and Leases Receivable Disclosure [Line Items]
Mortgage loans, net of allowances	$ 1,062	$ 1,104
Commercial mortgage loans | Hotels | Property Type Concentration Risk | Mortgage Loans, Net
Loans and Leases Receivable Disclosure [Line Items]
Percentage concentration risk	9.60%	10.50%
Commercial mortgage loans | Retail
Loans and Leases Receivable Disclosure [Line Items]
Mortgage loans, net of allowances	$ 2,117	$ 2,182
Commercial mortgage loans | Retail | Property Type Concentration Risk | Mortgage Loans, Net
Loans and Leases Receivable Disclosure [Line Items]
Percentage concentration risk	19.10%	20.80%
Commercial mortgage loans | Office building
Loans and Leases Receivable Disclosure [Line Items]
Mortgage loans, net of allowances	$ 3,465	$ 2,899
Commercial mortgage loans | Office building | Property Type Concentration Risk | Mortgage Loans, Net
Loans and Leases Receivable Disclosure [Line Items]
Percentage concentration risk	31.20%	27.60%
Commercial mortgage loans | Industrial
Loans and Leases Receivable Disclosure [Line Items]
Mortgage loans, net of allowances	$ 1,402	$ 1,448
Commercial mortgage loans | Industrial | Property Type Concentration Risk | Mortgage Loans, Net
Loans and Leases Receivable Disclosure [Line Items]
Percentage concentration risk	12.70%	13.80%
Commercial mortgage loans | Apartment
Loans and Leases Receivable Disclosure [Line Items]
Mortgage loans, net of allowances	$ 2,333	$ 2,142
Commercial mortgage loans | Apartment | Property Type Concentration Risk | Mortgage Loans, Net
Loans and Leases Receivable Disclosure [Line Items]
Percentage concentration risk	21.10%	20.40%
Commercial mortgage loans | Other commercial
Loans and Leases Receivable Disclosure [Line Items]
Mortgage loans, net of allowances	$ 699	$ 730
Commercial mortgage loans | Other commercial | Property Type Concentration Risk | Mortgage Loans, Net
Loans and Leases Receivable Disclosure [Line Items]
Percentage concentration risk	6.30%	6.90%