Derivatives and Hedge Accounting Activities (Schedule of Amounts Recorded on Balance Sheet Related to Cumulative Basis Adjustments for Fair Value Hedges) (Detail) - Designated as Hedging Instrument - Fair Value Hedging - Long-term Debt - USD ($) $ in Millions		Dec. 31, 2020	Dec. 31, 2019
Derivative Instruments And Hedging Activities Disclosures [Line Items]
Carrying Amount of the Hedged Asset (Liability)	[1]	$ (1,153)	$ (1,154)
Cumulative Amount of Fair Value Hedging Adjustments Included in the Carrying Amount of the Hedged(Liabilities)	[2]	$ (3)	$ (4)

[1] Includes $(1,153) million and $(397) million related to discontinued hedging relationships at December 31, 2020 and December 31, 2019,             respectively.

[2] Includes $(3) million and $3 million of hedging adjustments on discontinued hedging relationships at December 31, 2020 and December 31,          2019, respectively.