Investments - Mortgage Loans, Net by Property Type and Geographic Region (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Loans and Leases Receivable Disclosure [Line Items]
Mortgage loans, net of allowances	$ 12,199	$ 10,631
Commercial mortgage loans
Loans and Leases Receivable Disclosure [Line Items]
Mortgage loans, net of allowances	$ 8,117	$ 7,297
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	$ 8,117	$ 7,297
Commercial mortgage loans | Total U.S. Region | Geographic Concentration Risk | Mortgage Loans, Net
Loans and Leases Receivable Disclosure [Line Items]
Percentage concentration risk	100.00%	100.00%
Commercial mortgage loans | East North Central
Loans and Leases Receivable Disclosure [Line Items]
Mortgage loans, net of allowances	$ 895	$ 855
Commercial mortgage loans | East North Central | Geographic Concentration Risk | Mortgage Loans, Net
Loans and Leases Receivable Disclosure [Line Items]
Percentage concentration risk	11.00%	11.70%
Commercial mortgage loans | East South Central
Loans and Leases Receivable Disclosure [Line Items]
Mortgage loans, net of allowances	$ 169	$ 295
Commercial mortgage loans | East South Central | Geographic Concentration Risk | Mortgage Loans, Net
Loans and Leases Receivable Disclosure [Line Items]
Percentage concentration risk	2.10%	4.00%
Commercial mortgage loans | Middle Atlantic
Loans and Leases Receivable Disclosure [Line Items]
Mortgage loans, net of allowances	$ 1,488	$ 1,131
Commercial mortgage loans | Middle Atlantic | Geographic Concentration Risk | Mortgage Loans, Net
Loans and Leases Receivable Disclosure [Line Items]
Percentage concentration risk	18.30%	15.50%
Commercial mortgage loans | Mountain
Loans and Leases Receivable Disclosure [Line Items]
Mortgage loans, net of allowances	$ 675	$ 616
Commercial mortgage loans | Mountain | Geographic Concentration Risk | Mortgage Loans, Net
Loans and Leases Receivable Disclosure [Line Items]
Percentage concentration risk	8.30%	8.40%
Commercial mortgage loans | New England
Loans and Leases Receivable Disclosure [Line Items]
Mortgage loans, net of allowances	$ 349	$ 374
Commercial mortgage loans | New England | Geographic Concentration Risk | Mortgage Loans, Net
Loans and Leases Receivable Disclosure [Line Items]
Percentage concentration risk	4.30%	5.10%
Commercial mortgage loans | Pacific
Loans and Leases Receivable Disclosure [Line Items]
Mortgage loans, net of allowances	$ 1,813	$ 1,540
Commercial mortgage loans | Pacific | Geographic Concentration Risk | Mortgage Loans, Net
Loans and Leases Receivable Disclosure [Line Items]
Percentage concentration risk	22.40%	21.10%
Commercial mortgage loans | South Atlantic
Loans and Leases Receivable Disclosure [Line Items]
Mortgage loans, net of allowances	$ 1,729	$ 1,468
Commercial mortgage loans | South Atlantic | Geographic Concentration Risk | Mortgage Loans, Net
Loans and Leases Receivable Disclosure [Line Items]
Percentage concentration risk	21.30%	20.20%
Commercial mortgage loans | West North Central
Loans and Leases Receivable Disclosure [Line Items]
Mortgage loans, net of allowances	$ 177	$ 173
Commercial mortgage loans | West North Central | Geographic Concentration Risk | Mortgage Loans, Net
Loans and Leases Receivable Disclosure [Line Items]
Percentage concentration risk	2.20%	2.40%
Commercial mortgage loans | West South Central
Loans and Leases Receivable Disclosure [Line Items]
Mortgage loans, net of allowances	$ 822	$ 845
Commercial mortgage loans | West South Central | Geographic Concentration Risk | Mortgage Loans, Net
Loans and Leases Receivable Disclosure [Line Items]
Percentage concentration risk	10.10%	11.60%
Commercial mortgage loans | Hotels
Loans and Leases Receivable Disclosure [Line Items]
Mortgage loans, net of allowances	$ 959	$ 1,040
Commercial mortgage loans | Hotels | Property Type Concentration Risk | Mortgage Loans, Net
Loans and Leases Receivable Disclosure [Line Items]
Percentage concentration risk	11.80%	14.30%
Commercial mortgage loans | Retail
Loans and Leases Receivable Disclosure [Line Items]
Mortgage loans, net of allowances	$ 1,553	$ 1,660
Commercial mortgage loans | Retail | Property Type Concentration Risk | Mortgage Loans, Net
Loans and Leases Receivable Disclosure [Line Items]
Percentage concentration risk	19.10%	22.70%
Commercial mortgage loans | Office building
Loans and Leases Receivable Disclosure [Line Items]
Mortgage loans, net of allowances	$ 2,650	$ 2,221
Commercial mortgage loans | Office building | Property Type Concentration Risk | Mortgage Loans, Net
Loans and Leases Receivable Disclosure [Line Items]
Percentage concentration risk	32.60%	30.50%
Commercial mortgage loans | Industrial
Loans and Leases Receivable Disclosure [Line Items]
Mortgage loans, net of allowances	$ 1,246	$ 1,196
Commercial mortgage loans | Industrial | Property Type Concentration Risk | Mortgage Loans, Net
Loans and Leases Receivable Disclosure [Line Items]
Percentage concentration risk	15.40%	16.40%
Commercial mortgage loans | Apartment
Loans and Leases Receivable Disclosure [Line Items]
Mortgage loans, net of allowances	$ 1,352	$ 791
Commercial mortgage loans | Apartment | Property Type Concentration Risk | Mortgage Loans, Net
Loans and Leases Receivable Disclosure [Line Items]
Percentage concentration risk	16.70%	10.80%
Commercial mortgage loans | Other commercial
Loans and Leases Receivable Disclosure [Line Items]
Mortgage loans, net of allowances	$ 357	$ 389
Commercial mortgage loans | Other commercial | Property Type Concentration Risk | Mortgage Loans, Net
Loans and Leases Receivable Disclosure [Line Items]
Percentage concentration risk	4.40%	5.30%
Residential mortgage loans
Loans and Leases Receivable Disclosure [Line Items]
Mortgage loans, net of allowances	$ 4,082	$ 3,334
Residential mortgage loans | Geographic Concentration Risk | Mortgage Loans, Net
Loans and Leases Receivable Disclosure [Line Items]
Percentage concentration risk	100.00%	100.00%
Residential mortgage loans | Total U.S. Region | Geographic Concentration Risk | Mortgage Loans, Net
Loans and Leases Receivable Disclosure [Line Items]
Percentage concentration risk	89.40%	100.00%
Residential mortgage loans | California | Geographic Concentration Risk | Mortgage Loans, Net
Loans and Leases Receivable Disclosure [Line Items]
Percentage concentration risk	29.60%	30.30%
Residential mortgage loans | Florida | Geographic Concentration Risk | Mortgage Loans, Net
Loans and Leases Receivable Disclosure [Line Items]
Percentage concentration risk	13.60%	16.30%
Residential mortgage loans | New York | Geographic Concentration Risk | Mortgage Loans, Net
Loans and Leases Receivable Disclosure [Line Items]
Percentage concentration risk	3.80%	7.70%
Residential mortgage loans | Other U.S. States | Geographic Concentration Risk | Mortgage Loans, Net
Loans and Leases Receivable Disclosure [Line Items]
Percentage concentration risk	36.90%	42.40%