Fair Value Hierarchy - Schedule of Level 3 Assets, and Ranges and Weighted Averages of Significant Unobservable Inputs (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
Level 3 | Loans and securities backed by real estate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Total financial assets at fair value | $	$ 171		$ 154
Level 3 | Loans and securities backed by real estate | Minimum | Yield
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	0.042		0.030
Level 3 | Loans and securities backed by real estate | Minimum | Recovery rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	0.427		0.358
Level 3 | Loans and securities backed by real estate | Minimum | Cumulative loss rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input			0.037
Level 3 | Loans and securities backed by real estate | Minimum | Duration (years)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	0.5		0.9
Level 3 | Loans and securities backed by real estate | Maximum | Yield
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	0.263		0.360
Level 3 | Loans and securities backed by real estate | Maximum | Recovery rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	0.760		0.761
Level 3 | Loans and securities backed by real estate | Maximum | Cumulative loss rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input			0.299
Level 3 | Loans and securities backed by real estate | Maximum | Duration (years)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	12.0		12.3
Level 3 | Loans and securities backed by real estate | Weighted Average | Yield
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	0.160		0.142
Level 3 | Loans and securities backed by real estate | Weighted Average | Recovery rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	0.488		0.547
Level 3 | Loans and securities backed by real estate | Weighted Average | Cumulative loss rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input			0.104
Level 3 | Loans and securities backed by real estate | Weighted Average | Duration (years)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	3.0		4.6
Level 3 | Corporate debt instruments
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Total financial assets at fair value | $	$ 1,316		$ 1,238
Level 3 | Corporate debt instruments | Minimum | Yield
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	0.037		0.011
Level 3 | Corporate debt instruments | Minimum | Recovery rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	0.070		0.115
Level 3 | Corporate debt instruments | Minimum | Duration (years)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	1.2		0.3
Level 3 | Corporate debt instruments | Maximum | Yield
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	0.404		0.343
Level 3 | Corporate debt instruments | Maximum | Recovery rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	0.700		0.770
Level 3 | Corporate debt instruments | Maximum | Duration (years)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	11.6		20.3
Level 3 | Corporate debt instruments | Weighted Average | Yield
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	0.102		0.069
Level 3 | Corporate debt instruments | Weighted Average | Recovery rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	0.457		0.480
Level 3 | Corporate debt instruments | Weighted Average | Duration (years)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	3.2		4.5
Level 3 | Other
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Total financial assets at fair value | $	$ 266		$ 342
Level 3 | Other | Minimum | Yield
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	0.062		0.028
Level 3 | Other | Minimum | Recovery rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	0.7		3.3
Level 3 | Other | Minimum | Duration (years)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	1.5		1.2
Level 3 | Other | Maximum | Yield
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	0.375		0.478
Level 3 | Other | Maximum | Recovery rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	5.1		4.5
Level 3 | Other | Maximum | Duration (years)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	9.6		14.4
Level 3 | Other | Weighted Average | Yield
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	0.166		0.100
Level 3 | Other | Weighted Average | Recovery rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	4.5		4.3
Level 3 | Other | Weighted Average | Duration (years)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement input	4.0		6.1