Long duration insurance contracts - Summary of periodic payment annuity and life and health Insurance benefits liabilities (Detail) - ASU 2018-12 [Member] - USD ($) $ in Millions	Jan. 01, 2021	Dec. 31, 2020
Liabilities for Guarantees on Long-Duration Contracts [Line Items]
Reclassifications to other policyholder liabilities		$ (1,215)
Balance at December 31, 2020 after reclassifications	$ 20,401
Change in discount rate assumptions	8,000
Change in cash flow assumptions	435
Balance as of January 1, 2021	28,836
Previously Reported [Member]
Liabilities for Guarantees on Long-Duration Contracts [Line Items]
Balance at December 31, 2020, as previously reported	21,616
Balance as of January 1, 2021		21,616
Periodic Payment Annuities [Member]
Liabilities for Guarantees on Long-Duration Contracts [Line Items]
Reclassifications to other policyholder liabilities		(286)
Balance at December 31, 2020 after reclassifications	10,688
Change in discount rate assumptions	6,553
Change in cash flow assumptions	(117)
Balance as of January 1, 2021	17,124
Periodic Payment Annuities [Member] | Previously Reported [Member]
Liabilities for Guarantees on Long-Duration Contracts [Line Items]
Balance at December 31, 2020, as previously reported	10,974
Balance as of January 1, 2021		10,974
Life and Health [Member]
Liabilities for Guarantees on Long-Duration Contracts [Line Items]
Reclassifications to other policyholder liabilities		(929)
Balance at December 31, 2020 after reclassifications	9,713
Change in discount rate assumptions	1,447
Change in cash flow assumptions	552
Balance as of January 1, 2021	11,712
Life and Health [Member] | Previously Reported [Member]
Liabilities for Guarantees on Long-Duration Contracts [Line Items]
Balance at December 31, 2020, as previously reported	$ 10,642
Balance as of January 1, 2021		$ 10,642