Financial Derivative Instruments - Carrying Amount of Fair Value Hedges (Details) - USD ($)		Jun. 30, 2020	Jun. 30, 2019
Derivative [Line Items]
Deferred Gain (Loss) on Discontinuation of Interest Rate Fair Value Hedge		$ 18,000,000	$ 19,000,000
Designated as Hedging Instrument
Derivative [Line Items]
Derivative, Amount of Hedged Item		502,000,000	800,000,000
Short-term Debt | Designated as Hedging Instrument
Derivative [Line Items]
Derivative, Amount of Hedged Item		502,000,000	300,000,000
Long-term Debt | Designated as Hedging Instrument
Derivative [Line Items]
Derivative, Amount of Hedged Item		0	500,000,000
Cumulative fair value adjustment [Member] | Designated as Hedging Instrument
Derivative [Line Items]
Derivative, Amount of Hedged Item	[1]	20,000,000	19,000,000
Cumulative fair value adjustment [Member] | Short-term Debt | Designated as Hedging Instrument
Derivative [Line Items]
Derivative, Amount of Hedged Item	[1]	2,000,000	1,000,000
Cumulative fair value adjustment [Member] | Long-term Debt | Designated as Hedging Instrument
Derivative [Line Items]
Derivative, Amount of Hedged Item	[1]	$ 18,000,000	$ 18,000,000

[1] At June 30, 2020 and 2019, these amounts include the cumulative amount of fair value hedging adjustments remaining for which hedge accounting has been discontinued, of $18 million and $19 million, respectively.