Investments Investments - Equity Investments (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Schedule of Equity Method Investments [Line Items]
Equity Securities Excluded From Fair Value Table	$ 8		$ 8		$ 0
Equity Securities, FV-NI, Realized Gain (Loss)	0	$ 0
Real Estate [Member]
Schedule of Equity Method Investments [Line Items]
Other investments	28		28		16
Hedge Funds, Multi-strategy [Member]
Schedule of Equity Method Investments [Line Items]
Other investments	213		213		196
Interest Rate Contract [Member]
Schedule of Equity Method Investments [Line Items]
Other investments	77		77		78
Illiquid Investments [Member]
Schedule of Equity Method Investments [Line Items]
Other investments	75		75		65
Insurance Linked [Member]
Schedule of Equity Method Investments [Line Items]
Other investments	3		3		3
Equity [Member]
Schedule of Equity Method Investments [Line Items]
Other investments	93		93		73
Credit Index Product [Member]
Schedule of Equity Method Investments [Line Items]
Other investments	106		106		73
Private Equity Funds [Member]
Schedule of Equity Method Investments [Line Items]
Other investments	23		23		13
Emerging Market Debt [Member]
Schedule of Equity Method Investments [Line Items]
Other investments	38		38		25
Equity investments in pooled funds [Member]
Schedule of Equity Method Investments [Line Items]
Other investments	656		656		543
Priced Through Pricing Vendors [Member]
Schedule of Equity Method Investments [Line Items]
Other investments	115		115		89
Priced Through Pricing Vendors [Member] | Interest Rate Contract [Member]
Schedule of Equity Method Investments [Line Items]
Other investments	0		0		3
Priced Through Pricing Vendors [Member] | Equity [Member]
Schedule of Equity Method Investments [Line Items]
Other investments	77		77		60
Priced Through Pricing Vendors [Member] | Emerging Market Debt [Member]
Schedule of Equity Method Investments [Line Items]
Other investments	38		38		$ 25
Gains (losses) on securities held as of reporting date [Member]
Schedule of Equity Method Investments [Line Items]
Equity Securities, FV-NI, Realized Gain (Loss)			2	$ (19)
Commitments [Member] | Partnership Interest [Member]
Schedule of Equity Method Investments [Line Items]
Other investments	$ 90		$ 90