Fair Values of Assets and Liabilities - Losses Recognized Related to Nonrecurring Fair Value Measurements of Individual Assets or Portfolios (Detail) - Fair Value, Measurements, Nonrecurring [Member] - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Loans [Member]
Fair Value Assets Measured On Nonrecurring Basis Losses Recognized [Line Items]
Losses recognized related to nonrecurring fair value measurements	$ 12	$ 55	$ 43	$ 60
Other Assets [Member]
Fair Value Assets Measured On Nonrecurring Basis Losses Recognized [Line Items]
Losses recognized related to nonrecurring fair value measurements	$ 5	$ 3	$ 6	$ 6