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		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Loans Receivable [Member]
Fair Value Assets Measured On Nonrecurring Basis Losses Recognized [Line Items]
Losses recognized related to nonrecurring fair value measurements	$ 25	$ 45	$ 66	$ 120
Other Assets [Member]
Fair Value Assets Measured On Nonrecurring Basis Losses Recognized [Line Items]
Losses recognized related to nonrecurring fair value measurements	$ 5	$ 3	$ 18	$ 15