Shareholders' Equity (Summary of Share Repurchases) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Shareholders' Equity [Abstract]
Total number of shares purchased (in millions)	2.0	5.0	5.9
Average price paid per share	$ 231.87	$ 159.87	$ 145.87
Total price paid (in millions)	$ 470.3	$ 795.5	$ 854.4

Equity impact of the cost of common and preferred stock that were repurchased during the period. Recorded using the cost method.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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