Fair Value Measurements (Level 3 Assets Measured at Fair Value on a Nonrecurring Basis) (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Jun. 30, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Goodwill, impairment loss		$ 579	$ 0	$ 0
Impairment of intangible assets, indefinite-lived (excluding goodwill)	$ 108
Impairment of intangible assets, finite-lived	60
Fair Value, Measurements, Nonrecurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Goodwill	315		0
Indefinite-lived intangible assets	384		0
Definite-lived intangible assets	0		0
Total level 3 assets	699		$ 0
Carrying amount | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Goodwill	894
Indefinite-lived intangible assets	492
Definite-lived intangible assets	60
Fair Value | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Goodwill	315
Indefinite-lived intangible assets	384
Definite-lived intangible assets	0
EMEA
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Goodwill, impairment loss	$ 579	$ 579