Risk Management - Interest Rate Risk Management (Details) - USD ($) $ in Millions	3 Months Ended
	Sep. 30, 2020	Mar. 31, 2020
Fixed-to-Variable Interest Rate Contracts | Designated as Hedging Instrument | Fair Value Hedging
Derivative [Line Items]
Notional amount	$ 7,625
Floating-to-Fixed Interest Rate Contracts | Designated as Hedging Instrument | Derivatives in cash flow hedging relationships
Derivative [Line Items]
Notional amount	250
Floating-to-Fixed Interest Rate Contracts | Derivatives not designated as hedging instruments | Fair Value Hedging
Derivative [Line Items]
Notional amount	3,500
Notional Amount	1,000	$ 2,500
Current Portion Of Debt | Fixed-to-Variable Interest Rate Contracts | Designated as Hedging Instrument
Derivative [Line Items]
Derivative, Amount of Hedged Item	900
Long-term Debt | Fixed-to-Variable Interest Rate Contracts | Designated as Hedging Instrument
Derivative [Line Items]
Derivative, Amount of Hedged Item	$ 6,725