Investments - Fair Value Measurement Inputs (Detail) $ in Millions	Sep. 30, 2021 USD ($) yr	Jun. 30, 2021 USD ($)	Dec. 31, 2020 USD ($) yr
Level 3 assets \| $	$ 733,616	$ 668,710	$ 627,073
Level 3 assets [Member]
Level 3 assets \| $	23,437	$ 25,623	26,305
Corporate debt securities [Member] \| Level 3 assets [Member] \| Investments [Member]
Level 3 assets \| $	$ 4,277		$ 5,286
Corporate debt securities [Member] \| Level 3 assets [Member] \| Yield [Member] \| Investments [Member] \| Maximum [Member]
Investments measurement input	14.60%		19.50%
Corporate debt securities [Member] \| Level 3 assets [Member] \| Yield [Member] \| Investments [Member] \| Minimum [Member]
Investments measurement input	6.90%		4.50%
Corporate debt securities [Member] \| Level 3 assets [Member] \| Yield [Member] \| Investments [Member] \| Weighted Average [Member]
Investments measurement input	9.80%		10.20%
Corporate debt securities [Member] \| Level 3 assets [Member] \| Recovery rate [Member] \| Investments [Member] \| Maximum [Member]
Investments measurement input	76.00%		70.00%
Corporate debt securities [Member] \| Level 3 assets [Member] \| Recovery rate [Member] \| Investments [Member] \| Minimum [Member]
Investments measurement input	9.10%		10.00%
Corporate debt securities [Member] \| Level 3 assets [Member] \| Recovery rate [Member] \| Investments [Member] \| Weighted Average [Member]
Investments measurement input	56.80%		50.70%
Corporate debt securities [Member] \| Level 3 assets [Member] \| Duration [Member] \| Investments [Member] \| Maximum [Member]
Investments measurement input	9.4		7.7
Corporate debt securities [Member] \| Level 3 assets [Member] \| Duration [Member] \| Investments [Member] \| Minimum [Member]
Investments measurement input	3.0		3.0
Corporate debt securities [Member] \| Level 3 assets [Member] \| Duration [Member] \| Investments [Member] \| Weighted Average [Member]
Investments measurement input	4.6		4.2
Corporate debt securities [Member] \| Level 3 assets [Member] \| Multiples [Member] \| Investments [Member] \| Maximum [Member]
Investments measurement input	36.1		29.3
Corporate debt securities [Member] \| Level 3 assets [Member] \| Multiples [Member] \| Investments [Member] \| Minimum [Member]
Investments measurement input	0.5		0.6
Corporate debt securities [Member] \| Level 3 assets [Member] \| Multiples [Member] \| Investments [Member] \| Weighted Average [Member]
Investments measurement input	8.2		6.9
Securities backed by real estate [Member] \| Level 3 assets [Member] \| Investments [Member]
Level 3 assets \| $	$ 1,088		$ 998
Securities backed by real estate [Member] \| Level 3 assets [Member] \| Yield [Member] \| Investments [Member] \| Maximum [Member]
Investments measurement input	20.30%		52.40%
Securities backed by real estate [Member] \| Level 3 assets [Member] \| Yield [Member] \| Investments [Member] \| Minimum [Member]
Investments measurement input	8.30%		8.20%
Securities backed by real estate [Member] \| Level 3 assets [Member] \| Yield [Member] \| Investments [Member] \| Weighted Average [Member]
Investments measurement input	13.50%		17.50%
Securities backed by real estate [Member] \| Level 3 assets [Member] \| Recovery rate [Member] \| Investments [Member] \| Maximum [Member]
Investments measurement input	69.00%		57.80%
Securities backed by real estate [Member] \| Level 3 assets [Member] \| Recovery rate [Member] \| Investments [Member] \| Minimum [Member]
Investments measurement input	56.80%		21.60%
Securities backed by real estate [Member] \| Level 3 assets [Member] \| Recovery rate [Member] \| Investments [Member] \| Weighted Average [Member]
Investments measurement input	59.90%		33.70%
Securities backed by real estate [Member] \| Level 3 assets [Member] \| Duration [Member] \| Investments [Member] \| Maximum [Member]
Investments measurement input	2.8		3.6
Securities backed by real estate [Member] \| Level 3 assets [Member] \| Duration [Member] \| Investments [Member] \| Minimum [Member]
Investments measurement input	0.4		0.4
Securities backed by real estate [Member] \| Level 3 assets [Member] \| Duration [Member] \| Investments [Member] \| Weighted Average [Member]
Investments measurement input	1.4		2.7
Other debt obligations [Member] \| Level 3 assets [Member] \| Investments [Member]
Level 3 assets \| $	$ 387		$ 497
Other debt obligations [Member] \| Level 3 assets [Member] \| Yield [Member] \| Investments [Member] \| Maximum [Member]
Investments measurement input	10.10%		6.20%
Other debt obligations [Member] \| Level 3 assets [Member] \| Yield [Member] \| Investments [Member] \| Minimum [Member]
Investments measurement input	2.20%		1.70%
Other debt obligations [Member] \| Level 3 assets [Member] \| Yield [Member] \| Investments [Member] \| Weighted Average [Member]
Investments measurement input	2.90%		3.50%
Other debt obligations [Member] \| Level 3 assets [Member] \| Duration [Member] \| Investments [Member] \| Maximum [Member]
Investments measurement input	6.3		10.3
Other debt obligations [Member] \| Level 3 assets [Member] \| Duration [Member] \| Investments [Member] \| Minimum [Member]
Investments measurement input	1.2		0.2
Other debt obligations [Member] \| Level 3 assets [Member] \| Duration [Member] \| Investments [Member] \| Weighted Average [Member]
Investments measurement input	4.3		6.4
Equity Securities [Member] \| Level 3 assets [Member] \| Investments [Member]
Level 3 assets \| $	$ 7,927		$ 9,642
Equity Securities [Member] \| Level 3 assets [Member] \| Multiples [Member] \| Investments [Member] \| Maximum [Member]
Investments measurement input	23.2		27.9
Equity Securities [Member] \| Level 3 assets [Member] \| Multiples [Member] \| Investments [Member] \| Minimum [Member]
Investments measurement input	0.4		0.6
Equity Securities [Member] \| Level 3 assets [Member] \| Multiples [Member] \| Investments [Member] \| Weighted Average [Member]
Investments measurement input	10.8		9.0
Equity Securities [Member] \| Level 3 assets [Member] \| Discount rate/yield [Member] \| Investments [Member] \| Maximum [Member]
Investments measurement input	54.20%		38.50%
Equity Securities [Member] \| Level 3 assets [Member] \| Discount rate/yield [Member] \| Investments [Member] \| Minimum [Member]
Investments measurement input	4.80%		4.00%
Equity Securities [Member] \| Level 3 assets [Member] \| Discount rate/yield [Member] \| Investments [Member] \| Weighted Average [Member]
Investments measurement input	15.90%		13.50%
Equity Securities [Member] \| Level 3 assets [Member] \| Capitalization rate [Member] \| Investments [Member] \| Maximum [Member]
Investments measurement input	14.00%		14.10%
Equity Securities [Member] \| Level 3 assets [Member] \| Capitalization rate [Member] \| Investments [Member] \| Minimum [Member]
Investments measurement input	4.20%		3.70%
Equity Securities [Member] \| Level 3 assets [Member] \| Capitalization rate [Member] \| Investments [Member] \| Weighted Average [Member]
Investments measurement input	6.30%		6.30%

Investments - Fair Value Measurement Inputs (Detail)
$ in Millions

Sep. 30, 2021

USD ($)

Jun. 30, 2021

USD ($)

Dec. 31, 2020

USD ($)

Level 3 assets | $

$ 733,616

$ 668,710

$ 627,073

Level 3 assets [Member]