Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Millions	3 Months Ended			9 Months Ended		12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Statement of Cash Flows [Abstract]
Net cash flows provided by (used in) operating activities				$ (1,792)	$ (664)
Fixed-maturity securities:
Purchases				(1,025)	(856)
Sales	$ 0		$ 137	222	627
Maturities and paydowns				757	642
Short-term investments with original maturities of over three months:
Purchases				0	(238)
Sales				0	41
Maturities and paydowns				32	198
Net sales (purchases) of short-term investments with original maturities of less than three months				125	415
Paydowns of financial guaranty variable interest entities’ assets				45	67
Purchases of other invested assets				(44)	(12)
Return of capital from and sales of other invested assets				61	21
Other				(4)	1
Net cash flows provided by (used in) investing activities				169	906
Financing activities
Dividends paid				(51)	(53)
Repurchases of common shares				(305)	(320)
Net paydowns of financial guaranty variable interest entities’ liabilities				(38)	(63)
Issuance of long-term debt, net of issuance costs				889	0
Redemptions and purchases of debt, including make-whole				(620)	(22)
Other				7	(12)
Cash flows from consolidated investment vehicles:
Proceeds from issuance of collateralized loan obligations				2,079	361
Repayment of collateralized loan obligations				(365)	0
Proceeds from issuance of warehouse financing debt				1,008	47
Repayment of warehouse financing debt				(1,061)	0
Contributions from noncontrolling interests to consolidated investment vehicles				33	69
Distributions to noncontrolling interests from consolidated investment vehicles				(10)	(19)
Net cash flows provided by (used in) financing activities				1,566	(12)
Effect of foreign exchange rate changes				(1)	(7)
Increase (decrease) in cash and restricted cash				(58)	223
Cash and restricted cash at beginning of period		$ 406		298	183	$ 183
Cash and restricted cash at end of period	240	298	406	240	406	298
Supplemental cash flow information
Income taxes				1	1
Interest on long-term debt				50	49
Reconciliation of cash and restricted cash to the condensed consolidated balance sheets:
Cash	101	162	223	101	223	162
Restricted cash (included in other assets)	1		1	1	1
Cash of consolidated investment vehicles (Note 9)	138		182	138	182
Cash and restricted cash at end of period	$ 240	$ 298	$ 406	$ 240	$ 406	$ 298