Accounting Principles and Practices - Schedule of Impact of Topic 606 on Cash Flow Statement (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Cash flows from operating activities
Net income	$ 153	$ 192	$ 821	$ 1,275
Deferred income taxes			(128)	(208)
Receivables, net			(11)	144
Accounts payable and accrued liabilities			(331)	(237)
Current income taxes			(137)	(785)
Other assets and liabilities			139	$ (39)
Accounting Standards Update 2014-09 | Adjustments
Cash flows from operating activities
Net income			(175)
Deferred income taxes			(16)
Receivables, net			244
Accounts payable and accrued liabilities			8
Current income taxes			(37)
Other assets and liabilities			(24)
Accounting Standards Update 2014-09 | Calculated under Revenue Guidance in Effect before Topic 606
Cash flows from operating activities
Net income			646
Deferred income taxes			(144)
Receivables, net			233
Accounts payable and accrued liabilities			(323)
Current income taxes			(174)
Other assets and liabilities			$ 115