Investments - Fair Value Measurement Inputs (Detail) $ in Millions	Jun. 30, 2021 USD ($) yr	Mar. 31, 2021 USD ($)	Dec. 31, 2020 USD ($) yr
Level 3 assets \| $	$ 668,710	$ 647,751	$ 627,073
Level 3 assets [Member]
Level 3 assets \| $	25,623	$ 26,893	26,305
Corporate debt securities [Member] \| Level 3 assets [Member] \| Investments [Member]
Level 3 assets \| $	$ 4,958		$ 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	7.00%		4.50%
Corporate debt securities [Member] \| Level 3 assets [Member] \| Yield [Member] \| Investments [Member] \| Weighted Average [Member]
Investments measurement input	9.40%		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	59.90%		50.70%
Corporate debt securities [Member] \| Level 3 assets [Member] \| Duration [Member] \| Investments [Member] \| Maximum [Member]
Investments measurement input	7.3		7.7
Corporate debt securities [Member] \| Level 3 assets [Member] \| Duration [Member] \| Investments [Member] \| Minimum [Member]
Investments measurement input	2.6		3.0
Corporate debt securities [Member] \| Level 3 assets [Member] \| Duration [Member] \| Investments [Member] \| Weighted Average [Member]
Investments measurement input	4.4		4.2
Corporate debt securities [Member] \| Level 3 assets [Member] \| Multiples [Member] \| Investments [Member] \| Maximum [Member]
Investments measurement input	20.9		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	7.6		6.9
Securities backed by real estate [Member] \| Level 3 assets [Member] \| Investments [Member]
Level 3 assets \| $	$ 1,117		$ 998
Securities backed by real estate [Member] \| Level 3 assets [Member] \| Yield [Member] \| Investments [Member] \| Maximum [Member]
Investments measurement input	28.20%		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	16.80%		17.50%
Securities backed by real estate [Member] \| Level 3 assets [Member] \| Recovery rate [Member] \| Investments [Member] \| Maximum [Member]
Investments measurement input	57.80%		57.80%
Securities backed by real estate [Member] \| Level 3 assets [Member] \| Recovery rate [Member] \| Investments [Member] \| Minimum [Member]
Investments measurement input	20.90%		21.60%
Securities backed by real estate [Member] \| Level 3 assets [Member] \| Recovery rate [Member] \| Investments [Member] \| Weighted Average [Member]
Investments measurement input	32.90%		33.70%
Securities backed by real estate [Member] \| Level 3 assets [Member] \| Duration [Member] \| Investments [Member] \| Maximum [Member]
Investments measurement input	3.2		3.6
Securities backed by real estate [Member] \| Level 3 assets [Member] \| Duration [Member] \| Investments [Member] \| Minimum [Member]
Investments measurement input	0.5		0.4
Securities backed by real estate [Member] \| Level 3 assets [Member] \| Duration [Member] \| Investments [Member] \| Weighted Average [Member]
Investments measurement input	3.1		2.7
Other debt obligations [Member] \| Level 3 assets [Member] \| Investments [Member]
Level 3 assets \| $	$ 502		$ 497
Other debt obligations [Member] \| Level 3 assets [Member] \| Yield [Member] \| Investments [Member] \| Maximum [Member]
Investments measurement input	9.60%		6.20%
Other debt obligations [Member] \| Level 3 assets [Member] \| Yield [Member] \| Investments [Member] \| Minimum [Member]
Investments measurement input	2.40%		1.70%
Other debt obligations [Member] \| Level 3 assets [Member] \| Yield [Member] \| Investments [Member] \| Weighted Average [Member]
Investments measurement input	4.30%		3.50%
Other debt obligations [Member] \| Level 3 assets [Member] \| Duration [Member] \| Investments [Member] \| Maximum [Member]
Investments measurement input	9.5		10.3
Other debt obligations [Member] \| Level 3 assets [Member] \| Duration [Member] \| Investments [Member] \| Minimum [Member]
Investments measurement input	1.3		0.2
Other debt obligations [Member] \| Level 3 assets [Member] \| Duration [Member] \| Investments [Member] \| Weighted Average [Member]
Investments measurement input	5.6		6.4
Equity Securities [Member] \| Level 3 assets [Member] \| Investments [Member]
Level 3 assets \| $	$ 9,755		$ 9,642
Equity Securities [Member] \| Level 3 assets [Member] \| Multiples [Member] \| Investments [Member] \| Maximum [Member]
Investments measurement input	33.8		27.9
Equity Securities [Member] \| Level 3 assets [Member] \| Multiples [Member] \| Investments [Member] \| Minimum [Member]
Investments measurement input	0.5		0.6
Equity Securities [Member] \| Level 3 assets [Member] \| Multiples [Member] \| Investments [Member] \| Weighted Average [Member]
Investments measurement input	12.1		9.0
Equity Securities [Member] \| Level 3 assets [Member] \| Discount rate/yield [Member] \| Investments [Member] \| Maximum [Member]
Investments measurement input	50.10%		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	15.40%		13.50%
Equity Securities [Member] \| Level 3 assets [Member] \| Capitalization rate [Member] \| Investments [Member] \| Maximum [Member]
Investments measurement input	13.10%		14.10%
Equity Securities [Member] \| Level 3 assets [Member] \| Capitalization rate [Member] \| Investments [Member] \| Minimum [Member]
Investments measurement input	3.80%		3.70%
Equity Securities [Member] \| Level 3 assets [Member] \| Capitalization rate [Member] \| Investments [Member] \| Weighted Average [Member]
Investments measurement input	6.20%		6.30%

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

Jun. 30, 2021

USD ($)

Mar. 31, 2021

USD ($)

Dec. 31, 2020

USD ($)

Level 3 assets | $

$ 668,710

$ 647,751

$ 627,073

Level 3 assets [Member]