Earnings Per Share (Narrative) (Details) $ / shares in Units, shares in Millions		1 Months Ended	12 Months Ended
	Aug. 02, 2019 USD ($) shares	Sep. 30, 2009 USD ($) $ / shares shares	Dec. 31, 2019 USD ($) shares	Dec. 31, 2018 shares	Dec. 31, 2017 shares
Debt Instrument [Line Items]
Undistributed earnings allocated to participating unvested share-based payment awards, weighted outstanding shares			4.6	4.9	5.2
Exchangeable Surplus Notes (in shares)			3.6	5.9	5.8
Long-term Debt | Exhangeable Surplus Notes
Debt Instrument [Line Items]
Debt Instrument, Face Amount | $		$ 500,000,000
Interest Rate		5.36%
Debt Instrument, Convertible, Conversion Ratio	12.3877	10.1235
Surplus notes principal amount, for each | $	$ 1,000	$ 1,000	$ 1,000
Exchangeable Surplus Notes (in shares)	6.2	5.1
Exchange price of common stock, per share | $ / shares		$ 98.78