Discontinued Operations (Communications Business Split-off) (Narrative) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	1 Months Ended	7 Months Ended	12 Months Ended
	Jul. 31, 2015	Jul. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Shares redeemed through the distribution of the communications business, value			$ 0.0	$ 0.0	$ 2,291.7
Discontinued operation, revenues prior Separation			$ 0.0	$ 3,029.8	$ 6,524.5
Discontinued operations | Communications business
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Shares held as Treasury shares	26.0				26.0
Shares redeemed through the distribution of the communications business, value	$ 2,300.0
Consideration of shares, number of shares received	62.5
Disposition of communications business, percentage of investment ownership	60.00%
Gain on disposition, net of tax					$ 767.0
Gain on disposition, income tax benefits					$ (6.0)
After-tax gain on disposition upon closing of transaction, per diluted share					$ 1.08
Discontinued operation, revenues prior Separation		$ 346.0