Equity, Stock Repurchase Activities (Details) $ / shares in Units, shares in Millions					12 Months Ended
	Oct. 24, 2017 $ / shares	Jul. 25, 2017 $ / shares	Apr. 25, 2017 $ / shares	Jan. 26, 2017 $ / shares	Dec. 31, 2017 USD ($) Dividend $ / shares shares	Dec. 31, 2016 USD ($) $ / shares shares	Dec. 31, 2015 USD ($) $ / shares shares	Feb. 28, 2017 USD ($)	Oct. 31, 2014 USD ($)	Feb. 28, 2014 USD ($)
Dividends
Per Share (in dollars per share) | $ / shares					$ 0.40	$ 0.40	$ 0.40
Dividends					$ 150,400,000	$ 152,500,000	$ 156,300,000
Stock Repurchase Program
Total of Dividends and Stock Repurchase Program, Amount					$ 870,100,000	$ 465,400,000	$ 1,298,800,000
Number of quarterly cash dividends declared | Dividend					4
Cash dividends declared per share of common stock (in dollars per share) | $ / shares	$ 0.10	$ 0.10	$ 0.10	$ 0.10	$ 0.40	$ 0.40	$ 0.40
Shares repurchased And retired related to net issuances					$ 6,000,000	$ 11,700,000	$ 11,100,000
Stock Repurchase Program 2014
Stock Repurchase Program
Shares | shares					26.1	13.5	45.4
Average price per share (in dollars per share) | $ / shares					$ 27.61	$ 23.25	$ 25.16
Amount					$ 719,700,000	$ 312,900,000	$ 1,142,500,000
Stock repurchase program, authorized amount								$ 4,400,000,000		$ 2,100,000,000
Additional amount authorized under Stock Repurchase Plan								$ 500,000,000	$ 1,800,000,000.0
Stock Repurchase Program 2014, Accelerated Share Repurchase
Stock Repurchase Program
Stock repurchase program, authorized amount										$ 1,200,000,000