Derivatives - Cash Flow Hedges (Details) - Cash flow hedge - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Mar. 31, 2020
Derivatives in Cash Flow Hedging Relationships
Accumulated other comprehensive income (loss), unrealized gain (loss) on cash flow hedges		$ (173)
Interest rate contracts
Derivatives in Cash Flow Hedging Relationships
Accumulated other comprehensive income (loss), unrealized gain (loss) on cash flow hedges			$ (143)
Derivative notional amount				$ 700
Additional derivative notional			$ 743	$ 1,200
Termination Of Derivative	$ 500
Treasury rate lock contracts
Derivatives in Cash Flow Hedging Relationships
Derivative notional amount					$ 500
Interest rate swap and treasury lock in aggregate
Derivatives in Cash Flow Hedging Relationships
Accumulated other comprehensive income (loss), unrealized gain (loss) on cash flow hedges		$ (107)
Foreign currency exchange contracts
Derivatives in Cash Flow Hedging Relationships
Maximum length of time hedged in cash flow hedge		36 months
After-tax net unrealized gain (loss) anticipated to be reclassified from AOCI to the income statement within next twelve months		$ (51)
After-tax net unrealized gain (loss) anticipated to be reclassified from AOCI to the income statement after the next fiscal year		(23)
After-tax unrealized gain (loss) anticipated to be reclassified from AOCI to the income statement after two fiscal years		$ (99)