Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Fixed income securities, amortized cost	$ 3,187	$ 3,451
Other Investments	$ 478	$ 391
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	20,000,000	20,000,000
Preferred Stock, Shares Issued	0	0
Preferred Stock, Shares Outstanding	0	0
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	130,000,000	130,000,000
Common stock, shares issued	45,571,743	45,365,170
Common Stock, Shares, Outstanding	45,555,400	45,336,278
Treasury stock, shares	16,343	28,892
Fixed Income Securities [Member]
Fixed income securities, amortized cost	$ 2,450	$ 3,021
Equity investments in pooled funds [Member]
Other Investments	432
Other Investment Not Readily Marketable, Fair Value	432	351
Collateral Pledged [Member] | Fixed Income Securities [Member]
Fixed income securities, amortized cost	85	0
Parent Company [Member]
Fixed income securities, amortized cost	71	151
Other Investments	$ 46	$ 40
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	20,000,000	20,000,000
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	130,000,000	130,000,000
Short-term Investments [Member]
Fixed income securities, amortized cost	$ 653	$ 430
Short-term Investments [Member] | Collateral Pledged [Member] | Fixed Income Securities [Member]
Fixed income securities, amortized cost	85
Short-term Investments [Member] | Parent Company [Member]
Fixed income securities, amortized cost	318	193
Variable Interest Entity, Primary Beneficiary [Member]
Long-term Debt	$ 4,351	$ 5,269