Acquisitions and Dispositions of Businesses - Acquisitions (Details) $ in Millions	9 Months Ended
	Sep. 30, 2019 USD ($) acquisition	Sep. 30, 2018 acquisition	Dec. 31, 2018 USD ($)
Business Acquisition [Line Items]
Number of business acquired under business combination | acquisition	3	5
Assets acquired
Goodwill	$ 8,071		$ 8,171
2019 Acquisitions
Business Combination, Consideration Transferred [Abstract]
Consideration Transferred	42
Deferred and contingent consideration	8
Aggregate consideration transferred	50
Assets acquired
Cash and cash equivalents	4
Receivables, net	1
Goodwill	33
Intangible assets, net	22
Fixed assets, net	1
Other assets	13
Total assets acquired	74
Liabilities assumed
Current liabilities	18
Other non-current liabilities	6
Total liabilities assumed	24
Net assets acquired	$ 50