Investments - Amount of Level 3 Investments and Significant Unobservable Inputs Used to Value Such Investments (Detail) $ in Millions	Sep. 30, 2022 USD ($) yr	Jun. 30, 2022 USD ($)	Dec. 31, 2021 USD ($) yr
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Total financial assets at fair value | $	$ 694,838	$ 738,615	$ 715,812
Level 3 assets
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Total financial assets at fair value | $	29,275	$ 28,884	24,083
Corporate debt securities | Level 3 assets | Investments
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Total financial assets at fair value | $	$ 6,738		$ 4,527
Corporate debt securities | Level 3 assets | Yield | Investments | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Percentage of investments, measurement input	2.00%		2.00%
Corporate debt securities | Level 3 assets | Yield | Investments | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Percentage of investments, measurement input	21.80%		29.00%
Corporate debt securities | Level 3 assets | Yield | Investments | Weighted Average
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Percentage of investments, measurement input	11.80%		10.80%
Corporate debt securities | Level 3 assets | Recovery rate | Investments | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Percentage of investments, measurement input	9.10%		9.10%
Corporate debt securities | Level 3 assets | Recovery rate | Investments | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Percentage of investments, measurement input	78.50%		76.00%
Corporate debt securities | Level 3 assets | Recovery rate | Investments | Weighted Average
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Percentage of investments, measurement input	51.70%		59.10%
Corporate debt securities | Level 3 assets | Duration (years) | Investments | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investments, measurement input	1.2		1.4
Corporate debt securities | Level 3 assets | Duration (years) | Investments | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investments, measurement input	5.5		6.4
Corporate debt securities | Level 3 assets | Duration (years) | Investments | Weighted Average
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investments, measurement input	3.9		3.8
Corporate debt securities | Level 3 assets | Multiples | Investments | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investments, measurement input	1.9		0.5
Corporate debt securities | Level 3 assets | Multiples | Investments | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investments, measurement input	66.5		28.2
Corporate debt securities | Level 3 assets | Multiples | Investments | Weighted Average
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investments, measurement input	7.8		6.9
Securities backed by real estate | Level 3 assets | Investments
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Total financial assets at fair value | $	$ 912		$ 1,078
Securities backed by real estate | Level 3 assets | Yield | Investments | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Percentage of investments, measurement input	8.30%		8.30%
Securities backed by real estate | Level 3 assets | Yield | Investments | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Percentage of investments, measurement input	23.30%		20.30%
Securities backed by real estate | Level 3 assets | Yield | Investments | Weighted Average
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Percentage of investments, measurement input	15.40%		13.10%
Securities backed by real estate | Level 3 assets | Recovery rate | Investments | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Percentage of investments, measurement input			55.10%
Securities backed by real estate | Level 3 assets | Recovery rate | Investments | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Percentage of investments, measurement input			61.00%
Securities backed by real estate | Level 3 assets | Recovery rate | Investments | Weighted Average
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Percentage of investments, measurement input			56.40%
Securities backed by real estate | Level 3 assets | Duration (years) | Investments | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investments, measurement input	1.0		0.1
Securities backed by real estate | Level 3 assets | Duration (years) | Investments | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investments, measurement input	4.2		2.6
Securities backed by real estate | Level 3 assets | Duration (years) | Investments | Weighted Average
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investments, measurement input	4.1		1.2
Other debt obligations | Level 3 assets | Investments
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Total financial assets at fair value | $	$ 284		$ 382
Other debt obligations | Level 3 assets | Yield | Investments | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Percentage of investments, measurement input	5.00%		2.30%
Other debt obligations | Level 3 assets | Yield | Investments | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Percentage of investments, measurement input	20.00%		10.60%
Other debt obligations | Level 3 assets | Yield | Investments | Weighted Average
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Percentage of investments, measurement input	7.10%		3.20%
Other debt obligations | Level 3 assets | Duration (years) | Investments | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investments, measurement input	0.4		0.9
Other debt obligations | Level 3 assets | Duration (years) | Investments | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investments, measurement input	1.5		9.3
Other debt obligations | Level 3 assets | Duration (years) | Investments | Weighted Average
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investments, measurement input	1.3		4.8
Equity securities | Level 3 assets | Investments
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Total financial assets at fair value | $	$ 9,020		$ 7,915
Equity securities | Level 3 assets | Multiples | Investments | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investments, measurement input	0.4		0.4
Equity securities | Level 3 assets | Multiples | Investments | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investments, measurement input	34.4		30.5
Equity securities | Level 3 assets | Multiples | Investments | Weighted Average
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Investments, measurement input	9.0		10.1
Equity securities | Level 3 assets | Discount rate/yield | Investments | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Percentage of investments, measurement input	6.00%		2.00%
Equity securities | Level 3 assets | Discount rate/yield | Investments | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Percentage of investments, measurement input	38.50%		35.00%
Equity securities | Level 3 assets | Discount rate/yield | Investments | Weighted Average
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Percentage of investments, measurement input	14.70%		14.10%
Equity securities | Level 3 assets | Capitalization rate | Investments | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Percentage of investments, measurement input	4.00%		3.50%
Equity securities | Level 3 assets | Capitalization rate | Investments | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Percentage of investments, measurement input	10.80%		14.00%
Equity securities | Level 3 assets | Capitalization rate | Investments | Weighted Average
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Percentage of investments, measurement input	5.40%		5.70%