Derivative Instruments - Summary of Cumulative Hedging Adjustment for Fair Value Hedges Included in Carrying Value of Hedged Assets (Liabilities) (Detail) - Fair Value Hedges [Member] - Long-term Debt Securities [Member] - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Derivative Instruments, Gain (Loss) [Line Items]
Carrying amount of the hedged assets (liabilities), Long-term debt	$ 4,544	$ 4,584
Cumulative hedging Adjustment included in the carrying amount of the hedged assets (liabilities)	$ (48)	$ (8)