Securitization Activities - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Assets securitized in a non-cash exchange for loans and investments	$ 132	$ 185	$ 435	$ 391
Net Asset related to Other Continuing Involvement	83		83		$ 57
Notional amount related to Other Continuing Involvement	1,470		1,470		1,200
Fair Value of Retained Interests	3,850		3,850		3,350
Other Retained Interests [Member]
Fair Value of Retained Interests	159		$ 159		$ 149
Weighted average life (years)			2 years 7 months 6 days		3 years 3 months 18 days
Maximum Exposure to Adverse Changes in the value of Other retained interests	$ 159		$ 159		$ 149