Consolidated Statements of Changes in Stockholders' Equity (Parenthetical) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016	Sep. 30, 2016	Dec. 31, 2015
Stockholders' Equity Attributable to Parent	$ 10,165.2	$ 9,770.4	$ 9,579.8
Preferred Stock
Stockholders' Equity Attributable to Parent	882.0		882.0
Common Stock
Stockholders' Equity Attributable to Parent	408.6	408.6	408.6	$ 408.6
Series C Preferred Stock | Preferred Stock
Stockholders' Equity Attributable to Parent	388.5	388.5	388.5	388.5
Series D Preferred Stock | Preferred Stock
Stockholders' Equity Attributable to Parent	$ 493.5	$ 493.5	$ 493.5	$ 493.5