Income Taxes - Income Taxes (Details) € in Millions, $ in Millions		3 Months Ended		9 Months Ended		12 Months Ended
	Oct. 04, 2017 EUR (€)	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Dec. 31, 2018 USD ($)
Income Tax Disclosure [Abstract]
Provision for income taxes		$ 494	$ 508	$ 1,588	$ 870
Discrete tax benefits				1,000	1,300
Cash paid for income taxes, net of refunds		241	$ 200	692	$ 1,013	$ 863	$ 1,106
Tax contingencies		$ 3,800		3,800		$ 3,800		$ 3,400
Internal Revenue Service (IRS) | Domestic Tax Authority [Member]
Income Tax Examination [Line Items]
Tax examination, estimate of additional tax expense				$ 1,500
Luxembourg Tax Administration [Member] | Foreign Tax Authority [Member]
Income Tax Examination [Line Items]
Tax examination, estimate of additional tax expense | €	€ 250