Investments - Gross Unrealized Appreciation (Depreciation) on Debt Securities (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 22,268	$ 22,550
Unrealized Appreciation	1,648	852
Unrealized (Depreciation)	(55)	(474)
Total Fair Value	23,861	22,928
Run-off Settlement Annuity Business [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	2,267	2,264
Unrealized Appreciation	676	479
Unrealized (Depreciation)	(7)	(40)
Total Fair Value	2,936	2,703
Federal government and agency [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	522	507
Unrealized Appreciation	245	204
Unrealized (Depreciation)	0	(1)
Total Fair Value	767	710
State and local government [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	813	920
Unrealized Appreciation	85	66
Unrealized (Depreciation)	0	(1)
Total Fair Value	898	985
Foreign government [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	2,023	2,214
Unrealized Appreciation	218	155
Unrealized (Depreciation)	(2)	(7)
Total Fair Value	2,239	2,362
Corporate [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	18,406	18,403
Unrealized Appreciation	1,073	411
Unrealized (Depreciation)	(49)	(453)
Total Fair Value	19,430	18,361
Mortgage and other asset-backed [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	504	506
Unrealized Appreciation	27	16
Unrealized (Depreciation)	(4)	(12)
Total Fair Value	$ 527	$ 510