Short-term Financing (Details) - USD ($)	3 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Jun. 30, 2018
Short-term Debt [Line Items]
Short-term debt	$ 0
Commercial paper	$ 0
Maturities of short-term funding agreements	overnight to up to five business days
Obligations under reverse repurchase agreements (A)	$ 453,000,000		$ 0
364-day credit agreement
Short-term Debt [Line Items]
Maximum borrowing capacity under credit facilities	$ 3,800,000,000
Term of credit agreement	364 days
Expiration date of credit facilities	Jun. 16, 2019
Extension option term	1 year
Credit Facility Expiring In June 2022
Short-term Debt [Line Items]
Maximum borrowing capacity under credit facilities	$ 2,250,000,000
Term of credit agreement	5 years
Expiration date of credit facilities	Jun. 17, 2022
Line of credit facility potentially available increase in maximum borrowing capacity	$ 500,000,000
Credit Facility Expiring In June Two Thousand Twenty Three [Member]
Short-term Debt [Line Items]
Maximum borrowing capacity under credit facilities	$ 3,750,000,000
Term of credit agreement	5 years
Expiration date of credit facilities	Jun. 13, 2023
Line of credit facility potentially available increase in maximum borrowing capacity	$ 500,000,000
Commercial paper program
Short-term Debt [Line Items]
Short-term Debt, Maximum Borrowing Capacity	$ 9,800,000,000
Maturities of commercial paper range	overnight to up to 364 days
Short-term debt, average outstanding amount	$ 3,700,000,000	$ 3,800,000,000
Debt instrument, interest rate during period	2.00%	1.20%
Short Term Commercial Paper Program
Short-term Debt [Line Items]
Commercial paper weighted average maturity	2 days	2 days
Reverse repurchase agreements
Short-term Debt [Line Items]
Short-term debt, average outstanding amount	$ 495,100,000	$ 526,200,000
Debt instrument, interest rate during period	1.70%	1.10%