Acquisitions And Divestitures Acquisition of nuTonomy, Inc (Details) - USD ($)		12 Months Ended
	Nov. 21, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Business Acquisition [Line Items]
Payments to Acquire Interest in Joint Venture		$ 50,000,000	$ 3,000,000	$ 3,000,000
Goodwill		$ 1,944,000,000	$ 1,502,000,000	$ 1,531,000,000
nutonomy
Business Acquisition [Line Items]
Business Acquisition, Percentage of Voting Interests Acquired	100.00%
Business Combination, Maximum Total Consideration	$ 454,000,000
Deferred Compensation, Payable after three years	51,000,000
Business Combination, Consideration Transferred	308,000,000
Payments to Acquire Businesses, Gross	284,000,000
Business Combination, Consideration Transferred, Liabilities Incurred	109,000,000
Deferred Compensation, Payable after one year	7,000,000
Deferred compensation, payable after two years	51,000,000
Business Combination, Contingent Consideration Arrangements, Range of Outcomes, Value, High	$ 54,000,000
Contingent Consideration Period	3 years
Business Combination, Contingent Consideration Arrangements, Range of Outcomes, Value, Low	$ 0
Business Combination, Contingent Consideration, Liability	24,000,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill	102,000,000
Other assets purchased and liabilities assumed, net	(40,000,000)
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net	62,000,000
Goodwill	246,000,000
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net	$ 308,000,000