Investments - Additional Information (Details)	12 Months Ended
	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Concentration Risk [Line Items]
Fair Value, Concentration of Risk, Investments	$ 0	$ 0
AFS securities in an unrealized loss position	871
Percentage of AFS securities depressed less than 20% of cost or amortized cost	96.00%
Mortgage loans	$ 4,215,000,000	3,704,000,000
Carrying Value	$ 0	1,000,000	$ 1,000,000	$ 0
Number of loans with extensions or restructuring	0
LTV ratio	52.00%
LTV ratio at origination	61.00%
Loans serviced	$ 6,400,000,000	6,000,000,000.0
Loans serviced on behalf of third parties	3,500,000	3,600,000,000
Servicing rights	0	0
Maximum exposure to loss for variable interest	$ 1,100,000,000	1,000,000,000.0
Required collateral under securities lending	100.00%
Assets Held by Insurance Regulators	$ 2,300,000,000	2,200,000,000
Short-term investments	2,921,000,000	4,283,000,000
Income (Loss) from Equity Method Investments	267,000,000	214,000,000	168,000,000
Equity method investments	1,600,000,000
Commitments to fund limited partnership and alternative investments	$ 852,000,000
Aggregate investment income from limited partnerships and other alternative investments	10.00%
Net investment income	$ 1,951,000,000	1,780,000,000	1,603,000,000
Limited Partner [Member]
Concentration Risk [Line Items]
Total assets	329,400,000,000	311,000,000,000.0
Liabilities	191,200,000,000	187,700,000,000
Net investment income	618,000,000	773,000,000	1,900,000,000
Net income (loss)	13,400,000,000	12,300,000,000	$ 9,800,000,000
Fair Value Measured at Net Asset Value Per Share [Member]
Concentration Risk [Line Items]
Deposit Assets	$ 38,000,000	0
Minimum [Member]
Concentration Risk [Line Items]
Percentage of fair value received at sale under repurchase agreements	95.00%
Maximum
Concentration Risk [Line Items]
Term of security lending agreement	90 days
Variable Interest Entity, Not Primary Beneficiary [Member]
Concentration Risk [Line Items]
Commitments for variable interest	$ 851,000,000	718,000,000
Investments [Member]
Concentration Risk [Line Items]
Loans serviced on behalf of third parties, retained and reported as assets	$ 2,900,000,000	2,400,000,000
SEC Schedule, 12-09, Allowance, Loan and Lease Loss [Member]
Concentration Risk [Line Items]
Mortgage loans		$ 23,000,000
Number of loans with an allowance	0
Disposal Group, Held-for-sale, Not Discontinued Operations [Member]
Concentration Risk [Line Items]
Number of loans with an allowance		0
Number of loans held-for-sale	0
Commercial Loan [Member]
Concentration Risk [Line Items]
Mortgage loans	$ 4,215,000,000	$ 3,704,000,000
Carrying Value	0	1,000,000
Commercial Loan [Member] | Amortized Cost [Member]
Concentration Risk [Line Items]
Mortgage loans	4,200,000,000	3,700,000,000
U.S. Treasuries
Concentration Risk [Line Items]
Debt Securities, Available-for-sale, Restricted	$ 37,000,000	$ 47,000,000
Financial Services Sector [Member]
Concentration Risk [Line Items]
Largest exposure by sector, percent of invested assets	8.00%	7.00%
Municipal
Concentration Risk [Line Items]
Largest exposure by sector, percent of invested assets	18.00%	22.00%
CMBS
Concentration Risk [Line Items]
Largest exposure by sector, percent of invested assets	9.00%	8.00%
Mortgage loans | Commercial Loan [Member]
Concentration Risk [Line Items]
Mortgage loans past due by 90 days or more	0	0
Domestic [Member]
Concentration Risk [Line Items]
Collateral provided by borrowers under securities lending	102.00%
Non-domestic [Member]
Concentration Risk [Line Items]
Collateral provided by borrowers under securities lending	105.00%
Fixed maturities
Concentration Risk [Line Items]
Debt Securities, Available-for-sale, Restricted	$ 447,000,000
Short-term Investments [Member]
Concentration Risk [Line Items]
Short-term investments	$ 189,000,000
Government of United Kingdom [Member] | Debt Security, Government, Non-US [Member]
Concentration Risk [Line Items]
Largest exposure by issuer, percent of invested assets (less than)	1.00%
New York State Dormitory Authority [Member] | Municipal
Concentration Risk [Line Items]
Largest exposure by issuer, percent of invested assets (less than)	1.00%	1.00%
Wells Fargo & Company [Member]
Concentration Risk [Line Items]
Largest exposure by issuer, percent of invested assets (less than)	1.00%
New York Transitional Authority [Member] | Municipal
Concentration Risk [Line Items]
Largest exposure by issuer, percent of invested assets (less than)		1.00%
Commonwealth Massachusetts [Member] | Municipal
Concentration Risk [Line Items]
Largest exposure by issuer, percent of invested assets (less than)		1.00%