Income Taxes (Narrative) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended	9 Months Ended	12 Months Ended
	Dec. 31, 2017	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Income Tax Disclosure [Abstract]
Federal statutory rate	35.00%	21.00%	21.00%	24.50%	35.00%
Unrecognized tax benefits that would impact effective tax rate			$ 124
Unrecognized tax benefits, income tax penalties and interest expense			4	$ 2	$ (1)
Unrecognized tax benefits, income tax penalties and interest accrued		$ 23	27	23
Income taxes paid			650	680	1,420
Net operating losses and tax credits		$ (396)	(407)	(396)
Net income tax expense (benefit), tax reform	$ (43)		$ 0	$ (189)	$ 0
Net income tax expense (benefit), tax reform, per diluted share	$ (0.07)			$ (0.30)
Income tax expense (benefit), continuing operations, adjustment of deferred tax (asset) liability				$ (94)
Income tax expense (benefit) due to repatriation of foreign earnings and withholding taxes				(35)
Income tax benefit for repatriation of foreign earnings, prior periods				$ (130)
Amount of net operating losses and tax credits expiring over the next 5 years			Approximately half
Non-U.S. tax holiday tax rate reductions for certain foreign jurisdictions, expiration period in years			3 years