Summary of Significant Accounting Principles and Practices - Schedule of Topic 606 Impact on Cash Flows (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash flows from operating activities
Net income	$ 353	$ 153	$ 58	$ 610	$ (12)	$ 192	$ 778	$ 305	$ 1,174	$ 1,263	$ 1,430
Receivables, net									127	254	105
Accounts payable and accrued liabilities									25	96	53
Current income taxes									34	(914)	(42)
Other assets and liabilities									(2)	$ 8	$ (66)
Accounting Standards Update 2014-09 | Difference between Revenue Guidance in Effect before and after Topic 606
Cash flows from operating activities
Net income									(78)
Receivables, net									(49)
Accounts payable and accrued liabilities									8
Current income taxes									(34)
Other assets and liabilities									(55)
Accounting Standards Update 2014-09 | Calculated under Revenue Guidance in Effect before Topic 606
Cash flows from operating activities
Net income									1,096
Receivables, net									78
Accounts payable and accrued liabilities									33
Current income taxes									0
Other assets and liabilities									$ (57)