Investments Investments - Equity Investments (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Real Estate [Member]
Schedule of Equity Method Investments [Line Items]
Other investments	$ 16	$ 16
Hedge Funds, Multi-strategy [Member]
Schedule of Equity Method Investments [Line Items]
Other investments	210	196
Interest Rate Contract [Member]
Schedule of Equity Method Investments [Line Items]
Other investments	77	78
Illiquid Investments [Member]
Schedule of Equity Method Investments [Line Items]
Other investments	67	65
Insurance Linked [Member]
Schedule of Equity Method Investments [Line Items]
Other investments	3	3
Equity [Member]
Schedule of Equity Method Investments [Line Items]
Other investments	82	73
Credit Index Product [Member]
Schedule of Equity Method Investments [Line Items]
Other investments	98	73
Private Equity Funds [Member]
Schedule of Equity Method Investments [Line Items]
Other investments	14	13
Emerging Market Debt [Member]
Schedule of Equity Method Investments [Line Items]
Other investments	33	25
Equity investments in pooled funds [Member]
Schedule of Equity Method Investments [Line Items]
Other investments	600	543
Priced Through Pricing Vendors [Member]
Schedule of Equity Method Investments [Line Items]
Other investments	99	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	66	60
Priced Through Pricing Vendors [Member] | Emerging Market Debt [Member]
Schedule of Equity Method Investments [Line Items]
Other investments	33	$ 25
Commitments [Member] | Partnership Interest [Member]
Schedule of Equity Method Investments [Line Items]
Other investments	$ 102