Schedule I. Summary of Investments (Details) $ in Millions	Dec. 31, 2018 USD ($)
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost	$ 30,735
Fair Value	31,028
Amount Shown on Consolidated Balance Sheets	31,020
U.S. Treasuries
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost	651
Fair Value	738
Amount Shown on Consolidated Balance Sheets	738
State, municipalities and political subdivisions
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost	754
Fair Value	764
Amount Shown on Consolidated Balance Sheets	764
U.S. corporate public securities
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost	7,908
Fair Value	8,015
Amount Shown on Consolidated Balance Sheets	8,015
U.S. corporate private securities
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost	3,686
Fair Value	3,653
Amount Shown on Consolidated Balance Sheets	3,653
Foreign corporate public securities and foreign governments
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost	2,551
Fair Value	2,540
Amount Shown on Consolidated Balance Sheets	2,540
Foreign corporate private securities
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost	3,235
Fair Value	3,175
Amount Shown on Consolidated Balance Sheets	3,175
Residential mortgage-backed securities
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost	2,966
Fair Value	3,036
Amount Shown on Consolidated Balance Sheets	3,036
Commercial mortgage-backed securities
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost	1,917
Fair Value	1,905
Amount Shown on Consolidated Balance Sheets	1,905
Other asset-backed securities
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost	1,230
Fair Value	1,208
Amount Shown on Consolidated Balance Sheets	1,208
Total fixed maturities, including securities pledged
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost	24,898
Fair Value	25,034
Amount Shown on Consolidated Balance Sheets	25,034
Equity securities
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost	0
Fair Value	0
Amount Shown on Consolidated Balance Sheets	57
Mortgage loans on real estate
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost	4,918
Fair Value	4,983
Amount Shown on Consolidated Balance Sheets	4,918
Policy loans
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost	210
Fair Value	210
Amount Shown on Consolidated Balance Sheets	210
Short-term investments
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost	50
Fair Value	50
Amount Shown on Consolidated Balance Sheets	50
Limited partnerships/corporations
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost	583
Fair Value	583
Amount Shown on Consolidated Balance Sheets	583
Derivatives
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost	36
Fair Value	128
Amount Shown on Consolidated Balance Sheets	128
Other investments
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Line Items]
Cost	40
Fair Value	40
Amount Shown on Consolidated Balance Sheets	$ 40