Income Taxes - Income Taxes (Details) € in Millions, $ in Millions		3 Months Ended		12 Months Ended
	Oct. 04, 2017 EUR (€)	Mar. 31, 2019 USD ($)	Mar. 31, 2018 USD ($)	Mar. 31, 2019 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2018 USD ($)
Income Tax Disclosure [Abstract]
Provision for income taxes		$ 836	$ 287
Discrete tax benefits		261	368
Cash taxes paid, net of refunds		168	$ 513	$ 840	$ 1,224
Tax contingencies		3,600		$ 3,600		$ 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