Goodwill and Other Intangible Assets, net (Changes in Goodwill and Net Carrying Amount of Intangible Assets) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Goodwill [Roll Forward]
Goodwill, beginning of period			$ 5,196	$ 5,307	$ 5,307
Acquisitions			66		0
Asset impairment			0		(111)
Goodwill, end of period	$ 5,262		5,262		5,196
Intangible Assets [Roll Forward]
Intangible assets, net, beginning of period			12,279	12,400	12,400
Acquisitions			437		15
Asset impairment			0		(98)
Amortization	(12)	$ (20)	(28)	$ (30)	(38)
Intangible assets, net, end of period	$ 12,688		$ 12,688		$ 12,279