Short-term Financing (Details) - USD ($)	3 Months Ended		6 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Jun. 30, 2017
Short-term Debt [Line Items]
Short-term debt	$ 0		$ 0
Commercial paper	0		$ 0		$ 0
Maturities of short-term funding agreements			overnight to up to five business days
Obligations under reverse repurchase agreements	0		$ 0		$ 0
364-day credit agreement
Short-term Debt [Line Items]
Maximum borrowing capacity under credit facilities	3,500,000,000		$ 3,500,000,000
Term of credit agreement			364 days
Expiration date of credit facilities			Jun. 16, 2018
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		$ 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 maturing June 2021
Short-term Debt [Line Items]
Maximum borrowing capacity under credit facilities	3,750,000,000		$ 3,750,000,000
Term of credit agreement			5 years
Expiration date of credit facilities			Jun. 18, 2021
Line of credit facility potentially available increase in maximum borrowing capacity			$ 500,000,000
Commercial paper program
Short-term Debt [Line Items]
Aggregate amount of commercial paper issuable under the short-term commercial paper program			$ 9,500,000,000
Maturities of commercial paper range			overnight to up to 364 days
Short-term debt, average outstanding amount	$ 3,500,000,000	$ 4,200,000,000	$ 3,700,000,000	$ 4,200,000,000
Debt instrument, interest rate during period	1.20%	0.50%	1.20%	0.50%
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	$ 537,000,000	$ 267,600,000	$ 531,600,000	$ 313,400,000
Debt instrument, interest rate during period	1.20%	0.50%	1.10%	0.50%