Fair Values of Assets and Liabilities - Adjusted Carrying Values for Assets Measured at Fair Value on Nonrecurring Basis (Detail) - Fair Value, Measurements, Nonrecurring [Member] - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans	$ 247	$ 40
Other assets	15	57
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans	247	40
Other assets	$ 15	$ 57