Subsequent Event (Tables)

12 Months Ended

Dec. 31, 2018

Disclosure Of Nonadjusting Events After Reporting Period [Abstract]

Summary of Remaining Principal Amount of Unsecured Notes

The remaining principal amounts of the Company’s unsecured notes as at January 31, 2019 are:

As at January 31, 2019	US$ Principal Amount
5.70% due October 15, 2019		500
3.00% due August 15, 2022		500
3.80% due September 15, 2023		450
4.25% due April 15, 2027		1,061
5.25% due June 15, 2037		666
6.75% due November 15, 2039		1,400
4.45% due September 15, 2042		722
5.20% due September 15, 2043		300
5.40% due June 15, 2047		851
		6,450