Derivatives and Fair Value of Financial Instruments - Assets and Liabilities at Fair Value (Details) - USD ($) $ in Millions	3 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Assets:
Trading securities	$ 1,336	$ 1,576
Liabilities:
Decrease in contingent consideration liability	1
Commodities
Assets:
Margin account	15	20
Domestic equity securities
Assets:
Trading securities	632	752
Domestic debt securities
Assets:
Trading securities	268	439
Foreign equity securities
Assets:
Trading securities	218	319
Money market funds held in trading accounts
Assets:
Trading securities	146	10
High yield securities
Assets:
Trading securities	19	21
Foreign debt securities
Assets:
Trading securities	16
Recurring basis \| Level 1
Assets:
Total Assets	1,282	1,596
Liabilities:
Liabilities	4	6
Recurring basis \| Level 1 \| Commodities
Assets:
Derivatives	4	4
Liabilities:
Derivatives	4	6
Recurring basis \| Level 1 \| Domestic equity securities \| Short term investments
Assets:
Trading securities	632	752
Recurring basis \| Level 1 \| Domestic equity securities \| Other current assets
Assets:
Trading securities	32	35
Recurring basis \| Level 1 \| Domestic debt securities \| Short term investments
Assets:
Trading securities	215	438
Recurring basis \| Level 1 \| Foreign equity securities \| Short term investments
Assets:
Trading securities	218	319
Recurring basis \| Level 1 \| Foreign equity securities \| Other current assets
Assets:
Trading securities	3	4
Recurring basis \| Level 1 \| Money market funds held in trading accounts \| Short term investments
Assets:
Trading securities	146	10
Recurring basis \| Level 1 \| Money market funds held in trading accounts \| Other current assets
Assets:
Trading securities	5	5
Recurring basis \| Level 1 \| High yield securities \| Short term investments
Assets:
Trading securities	7	21
Recurring basis \| Level 1 \| Foreign debt securities \| Short term investments
Assets:
Trading securities	2
Recurring basis \| Level 1 \| Term deposits \| Short term investments
Assets:
Trading securities	9
Recurring basis \| Level 1 \| Other trading investments \| Short term investments
Assets:
Trading securities	5	6
Recurring basis \| Level 1 \| Fixed income securities \| Other current assets
Assets:
Trading securities	3	2
Recurring basis \| Level 1 \| Other \| Other current assets
Assets:
Trading securities	1
Recurring basis \| Level 2
Assets:
Total Assets	111	33
Liabilities:
Liabilities	5	6
Recurring basis \| Level 2 \| Commodities
Assets:
Derivatives	2
Recurring basis \| Level 2 \| Foreign currencies
Assets:
Derivatives	2	3
Liabilities:
Derivatives		6
Recurring basis \| Level 2 \| Domestic debt securities \| Short term investments
Assets:
Trading securities	53	1
Recurring basis \| Level 2 \| Collateralized loan obligations \| Short term investments
Assets:
Trading securities	28	29
Recurring basis \| Level 2 \| High yield securities \| Short term investments
Assets:
Trading securities	12
Recurring basis \| Level 2 \| Foreign debt securities \| Short term investments
Assets:
Trading securities	14
Recurring basis \| Level 2 \| Other trading investments \| Short term investments
Liabilities:
Liabilities	5
Recurring basis \| Level 3
Liabilities:
Contingent consideration	13
Liabilities	13
Recurring basis \| Fair Value
Assets:
Total Assets	1,393	1,629
Liabilities:
Contingent consideration	13
Liabilities	22	12
Recurring basis \| Fair Value \| Commodities
Assets:
Derivatives	6	4
Margin account	15	20
Derivative assets and liabilities, net basis	17	18
Liabilities:
Derivatives	4	6
Recurring basis \| Fair Value \| Foreign currencies
Assets:
Derivatives	2	3
Liabilities:
Derivatives		6
Recurring basis \| Fair Value \| Domestic equity securities \| Short term investments
Assets:
Trading securities	632	752
Recurring basis \| Fair Value \| Domestic equity securities \| Other current assets
Assets:
Trading securities	32	35
Recurring basis \| Fair Value \| Domestic debt securities \| Short term investments
Assets:
Trading securities	268	439
Recurring basis \| Fair Value \| Foreign equity securities \| Short term investments
Assets:
Trading securities	218	319
Recurring basis \| Fair Value \| Foreign equity securities \| Other current assets
Assets:
Trading securities	3	4
Recurring basis \| Fair Value \| Money market funds held in trading accounts \| Short term investments
Assets:
Trading securities	146	10
Recurring basis \| Fair Value \| Money market funds held in trading accounts \| Other current assets
Assets:
Trading securities	5	5
Recurring basis \| Fair Value \| Collateralized loan obligations \| Short term investments
Assets:
Trading securities	28	29
Recurring basis \| Fair Value \| High yield securities \| Short term investments
Assets:
Trading securities	19	21
Recurring basis \| Fair Value \| Foreign debt securities \| Short term investments
Assets:
Trading securities	16
Recurring basis \| Fair Value \| Term deposits \| Short term investments
Assets:
Trading securities	9
Recurring basis \| Fair Value \| Other trading investments \| Short term investments
Assets:
Trading securities	5	6
Liabilities:
Liabilities	5
Recurring basis \| Fair Value \| Fixed income securities \| Other current assets
Assets:
Trading securities	3	$ 2
Recurring basis \| Fair Value \| Other \| Other current assets
Assets:
Trading securities	$ 1

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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Amount of increase (decrease) in the value of a contingent consideration liability, including, but not limited to, differences arising upon settlement.

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The amount of cash or securities placed with a broker or counterparty as security for a trading or derivatives securities position which was partially obtained with funds provided by the broker dealer.

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