Fair Value Measurement - Financial Instruments Carried at Fair Value (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Assets:
Estimated Fair Value	$ 9,357	$ 9,624
Other invested assets	260	214
Assets of CIVs	4,371	1,913
Other assets	127	145
Liabilities:
Credit derivative liabilities	137	103
Liabilities of CIVs	3,886	1,590
Fixed-maturity securities
Assets:
Estimated Fair Value	8,663	8,773
Fixed-maturity securities | Obligations of state and political subdivisions
Assets:
Estimated Fair Value	3,853	3,991
Fixed-maturity securities | U.S. government and agencies
Assets:
Estimated Fair Value	131	162
Fixed-maturity securities | Corporate securities
Assets:
Estimated Fair Value	2,707	2,513
Fixed-maturity securities | RMBS
Assets:
Estimated Fair Value	484	566
Fixed-maturity securities | CMBS
Assets:
Estimated Fair Value	354	387
Fixed-maturity securities | Non-U.S. government securities
Assets:
Estimated Fair Value	137	173
Short-term investments
Assets:
Estimated Fair Value	694	851
Fair Value Measured at Net Asset Value Per Share
Assets:
Other invested assets	119	91
Fair Value Measured at Net Asset Value Per Share | Fund investments | Equity securities
Assets:
Assets of CIVs	9	8
Recurring
Assets:
Other invested assets	13	15
FG VIEs’ assets	271	296
Assets of CIVs	4,107	1,719
Other assets	127	145
Total assets carried at fair value	13,875	11,799
Liabilities:
Credit derivative liabilities	137	103
FG VIEs’ liabilities with recourse, at fair value	281	316
FG VIEs’ liabilities without recourse, at fair value	20	17
Liabilities of CIVs	3,243	1,299
Other liabilities		1
Total liabilities carried at fair value	3,681	1,736
Recurring | CLO obligations of CFEs
Liabilities:
Liabilities of CIVs	2,937	1,227
Recurring | Warehouse financing debt
Liabilities:
Liabilities of CIVs	275	25
Recurring | Securities sold short
Liabilities:
Liabilities of CIVs	31	47
Recurring | Fixed-maturity securities
Assets:
Estimated Fair Value	8,663	8,773
Recurring | Fixed-maturity securities | Obligations of state and political subdivisions
Assets:
Estimated Fair Value	3,853	3,991
Recurring | Fixed-maturity securities | U.S. government and agencies
Assets:
Estimated Fair Value	131	162
Recurring | Fixed-maturity securities | Corporate securities
Assets:
Estimated Fair Value	2,707	2,513
Recurring | Fixed-maturity securities | RMBS
Assets:
Estimated Fair Value	484	566
Recurring | Fixed-maturity securities | CMBS
Assets:
Estimated Fair Value	354	387
Recurring | Fixed-maturity securities | Asset-backed securities
Assets:
Estimated Fair Value	997	981
Recurring | Fixed-maturity securities | Non-U.S. government securities
Assets:
Estimated Fair Value	137	173
Recurring | Short-term investments
Assets:
Estimated Fair Value	694	851
Recurring | Fund investments | Obligations of state and political subdivisions
Assets:
Assets of CIVs	93	61
Recurring | Fund investments | Corporate securities
Assets:
Assets of CIVs		9
Recurring | Fund investments | Structured products
Assets:
Assets of CIVs	53	39
Recurring | Fund investments | Corporate securities
Assets:
Assets of CIVs	2
Recurring | Fund investments | Equity securities
Assets:
Assets of CIVs		10
Recurring | Fund investments | Equity securities
Assets:
Assets of CIVs	34
Recurring | Fund investments | Other
Assets:
Assets of CIVs	1
Recurring | CLO investments and CLO warehouse assets | Short-term investments
Assets:
Assets of CIVs	252	139
Recurring | CLO investments and CLO warehouse assets | Corporate securities
Assets:
Assets of CIVs	3,672	1,461
Recurring | Level 1
Assets:
Other invested assets	6	10
FG VIEs’ assets	0	0
Assets of CIVs	252	139
Other assets	50	42
Total assets carried at fair value	999	977
Liabilities:
Credit derivative liabilities	0	0
FG VIEs’ liabilities with recourse, at fair value	0	0
FG VIEs’ liabilities without recourse, at fair value	0	0
Liabilities of CIVs	0	0
Other liabilities		0
Total liabilities carried at fair value	0	0
Recurring | Level 1 | CLO obligations of CFEs
Liabilities:
Liabilities of CIVs	0	0
Recurring | Level 1 | Warehouse financing debt
Liabilities:
Liabilities of CIVs	0	0
Recurring | Level 1 | Securities sold short
Liabilities:
Liabilities of CIVs	0	0
Recurring | Level 1 | Fixed-maturity securities
Assets:
Estimated Fair Value	0	0
Recurring | Level 1 | Fixed-maturity securities | Obligations of state and political subdivisions
Assets:
Estimated Fair Value	0	0
Recurring | Level 1 | Fixed-maturity securities | U.S. government and agencies
Assets:
Estimated Fair Value	0	0
Recurring | Level 1 | Fixed-maturity securities | Corporate securities
Assets:
Estimated Fair Value	0	0
Recurring | Level 1 | Fixed-maturity securities | RMBS
Assets:
Estimated Fair Value	0	0
Recurring | Level 1 | Fixed-maturity securities | CMBS
Assets:
Estimated Fair Value	0	0
Recurring | Level 1 | Fixed-maturity securities | Asset-backed securities
Assets:
Estimated Fair Value	0	0
Recurring | Level 1 | Fixed-maturity securities | Non-U.S. government securities
Assets:
Estimated Fair Value	0	0
Recurring | Level 1 | Short-term investments
Assets:
Estimated Fair Value	691	786
Recurring | Level 1 | Fund investments | Obligations of state and political subdivisions
Assets:
Assets of CIVs	0	0
Recurring | Level 1 | Fund investments | Corporate securities
Assets:
Assets of CIVs		0
Recurring | Level 1 | Fund investments | Structured products
Assets:
Assets of CIVs	0	0
Recurring | Level 1 | Fund investments | Corporate securities
Assets:
Assets of CIVs	0
Recurring | Level 1 | Fund investments | Equity securities
Assets:
Assets of CIVs		0
Recurring | Level 1 | Fund investments | Equity securities
Assets:
Assets of CIVs	0
Recurring | Level 1 | Fund investments | Other
Assets:
Assets of CIVs	0
Recurring | Level 1 | CLO investments and CLO warehouse assets | Short-term investments
Assets:
Assets of CIVs	252	139
Recurring | Level 1 | CLO investments and CLO warehouse assets | Corporate securities
Assets:
Assets of CIVs	0	0
Recurring | Level 2
Assets:
Other invested assets	0	0
FG VIEs’ assets	0	0
Assets of CIVs	3,821	1,578
Other assets	51	48
Total assets carried at fair value	11,222	9,138
Liabilities:
Credit derivative liabilities	0	0
FG VIEs’ liabilities with recourse, at fair value	0	0
FG VIEs’ liabilities without recourse, at fair value	0	0
Liabilities of CIVs	247	72
Other liabilities		1
Total liabilities carried at fair value	247	73
Recurring | Level 2 | CLO obligations of CFEs
Liabilities:
Liabilities of CIVs	0	0
Recurring | Level 2 | Warehouse financing debt
Liabilities:
Liabilities of CIVs	216	25
Recurring | Level 2 | Securities sold short
Liabilities:
Liabilities of CIVs	31	47
Recurring | Level 2 | Fixed-maturity securities
Assets:
Estimated Fair Value	7,347	7,447
Recurring | Level 2 | Fixed-maturity securities | Obligations of state and political subdivisions
Assets:
Estimated Fair Value	3,743	3,890
Recurring | Level 2 | Fixed-maturity securities | U.S. government and agencies
Assets:
Estimated Fair Value	131	162
Recurring | Level 2 | Fixed-maturity securities | Corporate securities
Assets:
Estimated Fair Value	2,707	2,483
Recurring | Level 2 | Fixed-maturity securities | RMBS
Assets:
Estimated Fair Value	246	311
Recurring | Level 2 | Fixed-maturity securities | CMBS
Assets:
Estimated Fair Value	354	387
Recurring | Level 2 | Fixed-maturity securities | Asset-backed securities
Assets:
Estimated Fair Value	29	41
Recurring | Level 2 | Fixed-maturity securities | Non-U.S. government securities
Assets:
Estimated Fair Value	137	173
Recurring | Level 2 | Short-term investments
Assets:
Estimated Fair Value	3	65
Recurring | Level 2 | Fund investments | Obligations of state and political subdivisions
Assets:
Assets of CIVs	93	61
Recurring | Level 2 | Fund investments | Corporate securities
Assets:
Assets of CIVs		9
Recurring | Level 2 | Fund investments | Structured products
Assets:
Assets of CIVs	53	39
Recurring | Level 2 | Fund investments | Corporate securities
Assets:
Assets of CIVs	2
Recurring | Level 2 | Fund investments | Equity securities
Assets:
Assets of CIVs		8
Recurring | Level 2 | Fund investments | Equity securities
Assets:
Assets of CIVs	0
Recurring | Level 2 | Fund investments | Other
Assets:
Assets of CIVs	1
Recurring | Level 2 | CLO investments and CLO warehouse assets | Short-term investments
Assets:
Assets of CIVs	0	0
Recurring | Level 2 | CLO investments and CLO warehouse assets | Corporate securities
Assets:
Assets of CIVs	3,672	1,461
Recurring | Level 3
Assets:
Other invested assets	7	5
FG VIEs’ assets	271	296
Assets of CIVs	34	2
Other assets	26	55
Total assets carried at fair value	1,654	1,684
Liabilities:
Credit derivative liabilities	137	103
FG VIEs’ liabilities with recourse, at fair value	281	316
FG VIEs’ liabilities without recourse, at fair value	20	17
Liabilities of CIVs	2,996	1,227
Other liabilities		0
Total liabilities carried at fair value	3,434	1,663
Recurring | Level 3 | CLO obligations of CFEs
Liabilities:
Liabilities of CIVs	2,937	1,227
Recurring | Level 3 | Warehouse financing debt
Liabilities:
Liabilities of CIVs	59	0
Recurring | Level 3 | Securities sold short
Liabilities:
Liabilities of CIVs	0	0
Recurring | Level 3 | Fixed-maturity securities
Assets:
Estimated Fair Value	1,316	1,326
Recurring | Level 3 | Fixed-maturity securities | Obligations of state and political subdivisions
Assets:
Estimated Fair Value	110	101
Recurring | Level 3 | Fixed-maturity securities | U.S. government and agencies
Assets:
Estimated Fair Value	0	0
Recurring | Level 3 | Fixed-maturity securities | Corporate securities
Assets:
Estimated Fair Value	0	30
Recurring | Level 3 | Fixed-maturity securities | RMBS
Assets:
Estimated Fair Value	238	255
Recurring | Level 3 | Fixed-maturity securities | CMBS
Assets:
Estimated Fair Value	0	0
Recurring | Level 3 | Fixed-maturity securities | Asset-backed securities
Assets:
Estimated Fair Value	968	940
Recurring | Level 3 | Fixed-maturity securities | Non-U.S. government securities
Assets:
Estimated Fair Value	0	0
Recurring | Level 3 | Short-term investments
Assets:
Estimated Fair Value	0	0
Recurring | Level 3 | Fund investments | Obligations of state and political subdivisions
Assets:
Assets of CIVs	0	0
Recurring | Level 3 | Fund investments | Corporate securities
Assets:
Assets of CIVs		0
Recurring | Level 3 | Fund investments | Structured products
Assets:
Assets of CIVs	0	0
Recurring | Level 3 | Fund investments | Corporate securities
Assets:
Assets of CIVs	0
Recurring | Level 3 | Fund investments | Equity securities
Assets:
Assets of CIVs		2
Recurring | Level 3 | Fund investments | Equity securities
Assets:
Assets of CIVs	34
Recurring | Level 3 | Fund investments | Other
Assets:
Assets of CIVs	0
Recurring | Level 3 | CLO investments and CLO warehouse assets | Short-term investments
Assets:
Assets of CIVs	0	0
Recurring | Level 3 | CLO investments and CLO warehouse assets | Corporate securities
Assets:
Assets of CIVs	$ 0	$ 0