Short-Term Borrowings, Long-Term Debt and Available Credit Facilities Narrative (Details) $ in Millions		36 Months Ended	37 Months Ended	60 Months Ended
		Nov. 13, 2021	Mar. 31, 2019	Nov. 13, 2023	Sep. 30, 2019 USD ($)	Feb. 13, 2019 USD ($)	Dec. 31, 2018 USD ($)	Nov. 13, 2018 USD ($)	Sep. 30, 2018 USD ($)	Mar. 22, 2016 USD ($)	May 31, 2014 USD ($)
Short-term Debt [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity					$ 7,300
Revolving Credit Facilities due 2024 [Member]
Short-term Debt [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity					3,000			$ 3,000
Revolving Credit Facilities due 2024 [Member] | Forecast [Member]
Short-term Debt [Line Items]
Debt Instrument, Term				5 years
Revolving Credit Facilities due 2022 [Member]
Short-term Debt [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity					3,000			$ 3,000
Revolving Credit Facilities due 2022 [Member] | Forecast [Member]
Short-term Debt [Line Items]
Debt Instrument, Term		3 years
Revolving Credit Facilities due 2022 [Member]
Short-term Debt [Line Items]
Ratio of Indebtedness to Net Capital								0.60
Securities Sold under Agreements to Repurchase [Member] | Repurchase Agreements [Member]
Short-term Debt [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity					1,300
Percentage of outstanding amounts borrowed utilized as collateral						105.00%
Interest rate in addition to LIBOR						0.75%
Short-term borrowings and finance lease obligations					1,129	$ 1,300	$ 0		$ 1,300
Accounts and Notes Receivable [Member] | Securities Sold under Agreements to Repurchase [Member] | Repurchase Agreements [Member]
Short-term Debt [Line Items]
Line of Credit Facility, amount pledged as collateral					1,186
Fair Value, Inputs, Level 2 [Member]
Short-term Debt [Line Items]
Long-term Debt, Fair Value					$ 115		$ 5,775		$ 9,883
Term Loan Facility due 2020 [Member]
Short-term Debt [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	[1]									$ 4,500
Debt Instrument, Term	[1]		3 years
EID [Member] | Revolving Credit Facilities due 2024 [Member]
Short-term Debt [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity											$ 3,000
EID [Member] | Term Loan Facility due 2020 [Member]
Short-term Debt [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	[1]									$ 4,500

[1] The Term Loan Facility was amended in 2018 to extend the maturity date to June 2020 and, subsequently, the facility was repaid and terminated in May 2019.