Amount of the cost of borrowed funds accounted for as interest expense.

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Name:	us-gaap_InterestExpense
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Fair Value Measurements - Effect of Interest Rate Swap Contracts Designated as Cash Flow Hedges (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Total interest expense which reflects the effects of cash flow hedges		$ (503)	$ (589)	$ (597)
Hedged item		(20)
Derivative designated as hedging instrument		$ 5
Debt Instrument, Redemption, Period One
Debt Instrument [Line Items]
Hedged item	$ (20)
Derivative designated as hedging instrument	$ 19