Shareholders' Equity Shareholders' Equity (Narrative) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Equity Repurchases Authorized per Capital Plan	$ 440
Equity Repurchases per Capital Plan	$ 303
Stock Option
Common stock shares reserved for future issuance	7,900
Restricted Stock
Shares of non-vested restricted stock outstanding	1,591	1,910
Common Stock
Shares repurchased under equity repurchase program	6,800	5,300	5,400
Warrants
Number of warrants to purchase common stock outstanding	4,800
Number of shares of common stock issuable under outstanding warrants	3,900
Average exercise price for outstanding warrants	$ 29.47
Year of expiration for outstanding warrants	2018
Shares of common stock issued upon exercise of warrants	2,317	934	361
Common stock shares reserved for future issuance	3,900
Equity Repurchase Program | Common Stock
Shares repurchased under equity repurchase program	6,600	5,100	5,200
Average cost per share of shares repurchased under equity repurchase program	$ 46.09	$ 45.65	$ 47.91
Equity Repurchase Program | Warrants
Warrants repurchased under equity repurchase program		500
Average cost per warrant repurchased under the equity repurchase program		$ 20.70