Business Description and Summary of Significant Accounting Policies Net Excess Tax Benefits on Stock-based Compensation Awards (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended				12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accounting Standards Update [Abstract]
Effective Income Tax Rate Reconciliation, Share-based Compensation, Excess Tax Benefit, Amount	$ 24	$ 5	$ 5	$ 6	$ 40	$ 24	$ 34
Effective Income Tax Rate Reconciliation, Share-based Compensation, Excess Tax Benefit, Per Share Amount	$ 0.04	$ 0.01	$ 0.01	$ 0.01	$ 0.07