Goodwill, Customer Relationships and Other Intangible Assets (Details 5) $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Business acquisition
Total consideration to acquire businesses	$ 5	$ 39	$ 4
Goodwill acquired during period	$ 10,825	$ 49
Various business acquisitions
Business acquisition
Number of businesses acquired		3
Total consideration to acquire businesses		$ 53
Total consideration, deferred or contingent cash payments		future deferred or contingent cash payments of $14 million
Goodwill acquired during period		$ 49