Financial Derivative Instruments - Carrying Amount of Fair Value Hedges (Details) - USD ($)		Jun. 30, 2019	Jun. 30, 2018
Derivative [Line Items]
Deferred Gain (Loss) on Discontinuation of Interest Rate Fair Value Hedge		$ 19,000,000	$ 20,000,000
Designated as Hedging Instrument
Derivative [Line Items]
Derivative, Amount of Hedged Item		800,000,000	783,000,000
Short-term Debt | Designated as Hedging Instrument
Derivative [Line Items]
Derivative, Amount of Hedged Item		300,000,000	0
Long-term Debt | Designated as Hedging Instrument
Derivative [Line Items]
Derivative, Amount of Hedged Item		500,000,000	783,000,000
Cumulative fair value adjustment [Member] | Designated as Hedging Instrument
Derivative [Line Items]
Derivative, Amount of Hedged Item	[1]	19,000,000	4,000,000
Cumulative fair value adjustment [Member] | Short-term Debt | Designated as Hedging Instrument
Derivative [Line Items]
Derivative, Amount of Hedged Item	[1]	1,000,000	0
Cumulative fair value adjustment [Member] | Long-term Debt | Designated as Hedging Instrument
Derivative [Line Items]
Derivative, Amount of Hedged Item	[1]	$ 18,000,000	$ 4,000,000

[1] At June 30, 2019 and 2018, these amounts include the cumulative amount of fair value hedging adjustments remaining for which hedge accounting has been discontinued of $19 million and $20 million, respectively.