Accounting Principles and Practices - Schedule of Impact of Topic 606 on Cash Flow Statement (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Cash flows from operating activities
Net income	$ 58	$ 778	$ 668	$ 1,083
Deferred income taxes			(93)	(227)
Receivables, net			(371)	(25)
Accounts payable and accrued liabilities			(495)	(377)
Current income taxes			(144)	(25)
Other assets and liabilities			301	$ 30
Accounting Standards Update 2014-09 | Adjustments
Cash flows from operating activities
Net income			(259)
Deferred income taxes			(29)
Receivables, net			405
Accounts payable and accrued liabilities			8
Current income taxes			(46)
Other assets and liabilities			(79)
Accounting Standards Update 2014-09 | Calculated under Revenue Guidance in Effect before Topic 606
Cash flows from operating activities
Net income			409
Deferred income taxes			(122)
Receivables, net			34
Accounts payable and accrued liabilities			(487)
Current income taxes			(190)
Other assets and liabilities			$ 222