Investments Investments - Equity Investments (Details) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Schedule of Equity Method Investments [Line Items]
Equity Securities Excluded From Fair Value Table	$ 8	$ 0
Real Estate [Member]
Schedule of Equity Method Investments [Line Items]
Other investments	25	16
Hedge Funds, Multi-strategy [Member]
Schedule of Equity Method Investments [Line Items]
Other investments	219	196
Interest Rate Contract [Member]
Schedule of Equity Method Investments [Line Items]
Other investments	78	78
Illiquid Investments [Member]
Schedule of Equity Method Investments [Line Items]
Other investments	71	65
Insurance Linked [Member]
Schedule of Equity Method Investments [Line Items]
Other investments	2	3
Equity [Member]
Schedule of Equity Method Investments [Line Items]
Other investments	86	73
Credit Index Product [Member]
Schedule of Equity Method Investments [Line Items]
Other investments	108	73
Private Equity Funds [Member]
Schedule of Equity Method Investments [Line Items]
Other investments	20	13
Emerging Market Debt [Member]
Schedule of Equity Method Investments [Line Items]
Other investments	40	25
Equity investments in pooled funds [Member]
Schedule of Equity Method Investments [Line Items]
Other investments	650	543
Priced Through Pricing Vendors [Member]
Schedule of Equity Method Investments [Line Items]
Other investments	110	89
Priced Through Pricing Vendors [Member] | Interest Rate Contract [Member]
Schedule of Equity Method Investments [Line Items]
Other investments	0	3
Priced Through Pricing Vendors [Member] | Equity [Member]
Schedule of Equity Method Investments [Line Items]
Other investments	70	60
Priced Through Pricing Vendors [Member] | Emerging Market Debt [Member]
Schedule of Equity Method Investments [Line Items]
Other investments	40	$ 25
Commitments [Member] | Partnership Interest [Member]
Schedule of Equity Method Investments [Line Items]
Other investments	$ 95