Shareholders' Equity And Net Income Per Share Dividends (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended									12 Months Ended
	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Dividends Payable [Line Items]
Cash dividends declared per share		$ 0.29	$ 0.29	$ 0.29	$ 0.29	$ 0.25	$ 0.25	$ 0.25	$ 0.25	$ 1.16	$ 1	$ 1
Payments of Cash Dividends		$ 79	$ 79	$ 79	$ 80	$ 70	$ 71	$ 72	$ 73	$ 317	$ 286
Subsequent Event
Dividends Payable [Line Items]
Cash dividends declared per share	$ 0.29