Business Combinations and Divestitures - Acquisition Activity (Details) $ in Millions	12 Months Ended
	Dec. 31, 2014 USD ($) acquisition	Dec. 31, 2013 USD ($) acquisition	Dec. 31, 2015 USD ($)
Business Acquisition [Line Items]
Number of businesses acquired | acquisition	3	4
Goodwill	$ 4,671	$ 4,855	$ 4,451
Other
Business Acquisition [Line Items]
Purchase consideration	58	148
Liabilities assumed	1	15
Purchased intangibles assets	29	51
Goodwill	$ 30	$ 112