Summary of Significant Accounting Principles and Practices Schedule Of Change In Presentation (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Operating income	$ 489	$ 265	$ (118)	$ 343	$ 463	$ 368	$ 387	$ 420	$ 979	$ 1,638	$ 1,587
Other income (expense)									(39)	36	$ 100
Pension Plan | US And UK Pension Plans
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Defined benefit plan, settlements, benefit obligation									128	220
Accounting Standards Update 2017-06 | Adjustments
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Operating income									86	173
Other income (expense)									(86)	(173)
Accounting Standards Update 2017-06 | Pro Forma
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Operating income									1,065	1,811
Other income (expense)									$ (125)	$ (137)