Capital Stock (Cash Dividend Activity) (Details) - USD ($) $ / shares in Units, $ 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
Dividends, Cash [Abstract]
Declaration Date	Oct. 30, 2018	Jul. 24, 2018	Apr. 24, 2018	Jan. 30, 2018	Oct. 24, 2017	Jul. 25, 2017	Apr. 27, 2017	Feb. 22, 2017
Record Date	Dec. 05, 2018	Sep. 10, 2018	Jun. 08, 2018	Mar. 09, 2018	Dec. 05, 2017	Sep. 08, 2017	Jun. 09, 2017	Mar. 10, 2017
Payment Date	Dec. 21, 2018	Sep. 25, 2018	Jun. 25, 2018	Mar. 23, 2018	Dec. 21, 2017	Sep. 25, 2017	Jun. 23, 2017	Mar. 24, 2017
Cash Dividend per Share	$ 0.75	$ 0.75	$ 0.75	$ 0.75	$ 0.70	$ 0.70	$ 0.65	$ 0.65
Total	$ 193	$ 195	$ 196	$ 192	$ 180	$ 181	$ 172	$ 172	$ 776	$ 705	$ 684