Investments Investments - Equity Investments (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Real Estate [Member]
Schedule of Equity Method Investments [Line Items]
Other investments	$ 15	$ 16
Hedge Funds, Multi-strategy [Member]
Schedule of Equity Method Investments [Line Items]
Other investments	182	65
Interest Rate Contract [Member]
Schedule of Equity Method Investments [Line Items]
Other investments	53	176
Illiquid Investments [Member]
Schedule of Equity Method Investments [Line Items]
Other investments	57	51
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	33	55
Credit Index Product [Member]
Schedule of Equity Method Investments [Line Items]
Other investments	69	66
Private Equity Funds [Member]
Schedule of Equity Method Investments [Line Items]
Other investments	16	0
Emerging Market Debt [Member]
Schedule of Equity Method Investments [Line Items]
Other investments	23	0
Equity investments in pooled funds [Member]
Schedule of Equity Method Investments [Line Items]
Other investments	451	432
Priced Through Pricing Vendors [Member]
Schedule of Equity Method Investments [Line Items]
Other investments	60	136
Priced Through Pricing Vendors [Member] | Interest Rate Contract [Member]
Schedule of Equity Method Investments [Line Items]
Other investments	3	81
Priced Through Pricing Vendors [Member] | Equity [Member]
Schedule of Equity Method Investments [Line Items]
Other investments	33	55
Priced Through Pricing Vendors [Member] | Emerging Market Debt [Member]
Schedule of Equity Method Investments [Line Items]
Other investments	23	$ 0
Commitments [Member] | Partnership Interest [Member]
Schedule of Equity Method Investments [Line Items]
Other investments	$ 48