Fair Value Hierarchy - Amount of Level 3 Investments and Significant Unobservable Inputs Used to Value Such Investments (Detail) $ in Millions	Sep. 30, 2023 USD ($) yr	Jun. 30, 2023 USD ($)	Dec. 31, 2022 USD ($) yr
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Total financial assets at fair value | $	$ 758,400	$ 722,276	$ 650,966
Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Total financial assets at fair value | $	24,862	$ 25,945	26,048
Corporate debt securities | Level 3 | Investments
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Total financial assets at fair value | $	$ 6,950		$ 7,003
Corporate debt securities | Level 3 | Yield | Investments | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Percentage of investments, measurement input	6.40%		5.00%
Corporate debt securities | Level 3 | Yield | Investments | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Percentage of investments, measurement input	22.00%		21.80%
Corporate debt securities | Level 3 | Yield | Investments | Weighted Average
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Percentage of investments, measurement input	12.50%		11.60%
Corporate debt securities | Level 3 | Recovery rate | Investments | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Percentage of investments, measurement input	7.30%		10.00%
Corporate debt securities | Level 3 | Recovery rate | Investments | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Percentage of investments, measurement input	58.90%		70.00%
Corporate debt securities | Level 3 | Recovery rate | Investments | Weighted Average
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Percentage of investments, measurement input	28.10%		55.50%
Corporate debt securities | Level 3 | Duration (years) | Investments | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investments, measurement input | yr	0.7		1.3
Corporate debt securities | Level 3 | Duration (years) | Investments | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investments, measurement input | yr	5.0		5.7
Corporate debt securities | Level 3 | Duration (years) | Investments | Weighted Average
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investments, measurement input | yr	3.2		3.3
Corporate debt securities | Level 3 | Multiples | Investments | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investments, measurement input	0.9		1.8
Corporate debt securities | Level 3 | Multiples | Investments | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investments, measurement input	46.2		83.4
Corporate debt securities | Level 3 | Multiples | Investments | Weighted Average
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investments, measurement input	7.1		8.3
Securities backed by real estate | Level 3 | Investments
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Total financial assets at fair value | $	$ 772		$ 827
Securities backed by real estate | Level 3 | Yield | Investments | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Percentage of investments, measurement input	8.00%		8.00%
Securities backed by real estate | Level 3 | Yield | Investments | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Percentage of investments, measurement input	18.40%		20.30%
Securities backed by real estate | Level 3 | Yield | Investments | Weighted Average
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Percentage of investments, measurement input	13.30%		14.60%
Securities backed by real estate | Level 3 | Duration (years) | Investments | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investments, measurement input | yr	2.0		0.6
Securities backed by real estate | Level 3 | Duration (years) | Investments | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investments, measurement input | yr	3.1		4.2
Securities backed by real estate | Level 3 | Duration (years) | Investments | Weighted Average
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investments, measurement input | yr	3.1		4.1
Other debt obligations | Level 3 | Investments
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Total financial assets at fair value | $	$ 249		$ 256
Other debt obligations | Level 3 | Yield | Investments | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Percentage of investments, measurement input	7.90%		5.20%
Other debt obligations | Level 3 | Yield | Investments | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Percentage of investments, measurement input	9.20%		8.40%
Other debt obligations | Level 3 | Yield | Investments | Weighted Average
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Percentage of investments, measurement input	8.40%		7.40%
Equity securities | Level 3 | Investments
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Total financial assets at fair value | $	$ 9,358		$ 8,856
Equity securities | Level 3 | Multiples | Investments | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investments, measurement input	0.5		0.5
Equity securities | Level 3 | Multiples | Investments | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investments, measurement input	36		34.3
Equity securities | Level 3 | Multiples | Investments | Weighted Average
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investments, measurement input	8.6		8.3
Equity securities | Level 3 | Discount rate/yield | Investments | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Percentage of investments, measurement input	3.90%		5.40%
Equity securities | Level 3 | Discount rate/yield | Investments | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Percentage of investments, measurement input	25.20%		38.50%
Equity securities | Level 3 | Discount rate/yield | Investments | Weighted Average
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Percentage of investments, measurement input	12.60%		14.60%
Equity securities | Level 3 | Capitalization rate | Investments | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Percentage of investments, measurement input	4.50%		4.00%
Equity securities | Level 3 | Capitalization rate | Investments | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Percentage of investments, measurement input	10.80%		10.80%
Equity securities | Level 3 | Capitalization rate | Investments | Weighted Average
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Percentage of investments, measurement input	5.50%		5.40%