Derivatives and Hedging Activities - Cumulative Basis Adjustments on Fair Value Hedges (Details) - Long-term debt - Interest rate - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Derivatives, Fair Value [Line Items]
Carrying amount of hedged item	$ 9,222	$ 8,408
Hedge accounting basis adjustment	538	240
Derivatives Not Designated as Hedging Instruments
Derivatives, Fair Value [Line Items]
Hedge accounting basis adjustment	$ (9)	$ (9)