Investments Investments - Equity Investments (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Schedule of Equity Method Investments [Line Items]
Other investments	$ 363	$ 478
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	60	65
Interest Rate Contract [Member]
Schedule of Equity Method Investments [Line Items]
Other investments	57	176
Illiquid Investments [Member]
Schedule of Equity Method Investments [Line Items]
Other investments	47	51
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	58	55
Credit Index Product [Member]
Schedule of Equity Method Investments [Line Items]
Other investments	52	66
Private Equity Funds [Member]
Schedule of Equity Method Investments [Line Items]
Other investments	4	0
Emerging Market Debt [Member]
Schedule of Equity Method Investments [Line Items]
Other investments	16	0
Equity investments in pooled funds [Member]
Schedule of Equity Method Investments [Line Items]
Other investments	312	432
Priced Through Pricing Vendors [Member] | Interest Rate Contract [Member]
Schedule of Equity Method Investments [Line Items]
Other investments	17	81
Priced Through Pricing Vendors [Member] | Equity [Member]
Schedule of Equity Method Investments [Line Items]
Other investments	48	55
Priced Through Pricing Vendors [Member] | Emerging Market Debt [Member]
Schedule of Equity Method Investments [Line Items]
Other investments	16	$ 0
Commitments [Member] | Partnership Interest [Member]
Schedule of Equity Method Investments [Line Items]
Other investments	$ 76