Derivative Financial Instruments - Cash Flow and Fair Value Hedges (Details) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2020	Dec. 31, 2019
Cash flow hedges
Derivative [Line Items]
Net unrecognized after-tax gain (loss) on active hedges recorded in AOCI	$ 0	$ 0
Net unrecognized after-tax gain (loss) on terminated hedges recorded in AOCI (to be recognized in earnings through 2022)	(79)	(101)
Estimated portion of net after-tax gain (loss) on active and terminated hedges to be reclassified from AOCI into earnings during the next 12 months	(34)	(37)
Fair Value Hedges
Derivative [Line Items]
Unrecognized pre-tax net gain (loss) on terminated hedges (to be recognized as interest primarily through 2029)	(46)	(57)
Portion of pre-tax net gain (loss) on terminated hedges to be recognized as a change in interest during the next 12 months	$ (5)	$ (6)