Summary of Significant Accounting Policies Employee Benefit Plans (Details) $ in Millions	3 Months Ended	12 Months Ended
	Sep. 30, 2015 USD ($) shares	Dec. 31, 2019 USD ($) plan shares	Dec. 31, 2018 USD ($) shares	Dec. 31, 2017 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Securities at Net Asset Value		$ 21.6	$ 20.3
stock acquired during period value employee stock ownership plan	$ 34.0		50.0
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of net assets available for plan benefits at beginning of year		409.9
Fair value of net assets available for plan benefits at end of year		471.1	409.9
Net pretax amount recognized		6.8	(6.9)	$ 27.7
Estimated future cash contributions next year		$ 10.8
Employee savings and stock ownership plan, number of allocated shares | shares		15,378,368
Employee savings and stock ownership plan, number of allocated shares to employees | shares		11,417,966
Employees Savings and Stock Ownership Plan [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Defined contribution plan, cost recognized		$ 21.7	12.9	15.6
Other profit sharing plans [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Defined contribution plan, cost recognized		18.4	20.7	17.8
Cash and deferred incentive compensation [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Defined contribution plan, cost recognized		48.3	46.7	68.5
Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of net assets available for plan benefits at beginning of year		342.7
Fair value of net assets available for plan benefits at end of year		406.8	342.7
Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of net assets available for plan benefits at beginning of year		63.2
Fair value of net assets available for plan benefits at end of year		57.0	63.2
Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of net assets available for plan benefits at beginning of year		3.9
Fair value of net assets available for plan benefits at end of year		$ 7.2	3.9
Pension Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Number of benefit plans | plan		1
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Projected benefit obligation at beginning of year		$ 530.1	579.2	537.5
Interest cost		22.6	20.8	22.5
Actuarial (gains) losses		59.8	(44.4)	42.0
Benefits paid		(26.0)	(25.4)	(22.8)
Net increase (decrease) for the year		56.3	(49.1)	41.6
Projected benefit obligation at end of year		586.4	530.1	579.2
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of net assets available for plan benefits at beginning of year		430.2	453.7	427.1
Actual return on plan assets		82.1	(12.0)	44.5
Sponsor contributions		6.5	14.0	4.8
Benefits paid		(26.0)	(25.4)	(22.8)
Net increase (decrease) for year		62.5	(23.5)	26.6
Fair value of net assets available for plan benefits at end of year		492.8	430.2	453.7
Defined Benefit Plan, Funded (Unfunded) Status of Plan		(93.6)	(99.8)	(125.4)
Net cost		(3.0)	(6.6)	(5.0)
Net recognized loss		$ (140.5)	$ (137.1)	$ (142.0)
Settlement discount rates		3.35%	4.40%
Settlement discount rates		4.40%	3.70%	4.30%
Long-term rates of return on plans' assets		7.00%	7.00%	7.25%
Expected future benefit payments in year one		$ 29.5
Expected future benefit payments in year two		31.6
Expected future benefit payments in year three		31.8
Expected future benefit payments in year four		32.7
Expected future benefit payments in year five		33.0
Expected future benefit payments in five fiscal years thereafter		$ 168.4
Total investments		100.00%	100.00%
Pension Plans, Defined Benefit [Member] | Common shares of Company stock [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of net assets available for plan benefits at beginning of year		$ 58.2
Fair value of net assets available for plan benefits at end of year		$ 63.2	$ 58.2
Total investments		12.90%	13.50%
Pension Plans, Defined Benefit [Member] | Common shares of Company stock [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of net assets available for plan benefits at beginning of year		$ 58.2
Fair value of net assets available for plan benefits at end of year		63.2	$ 58.2
Pension Plans, Defined Benefit [Member] | Common shares of Company stock [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of net assets available for plan benefits at beginning of year		0.0
Fair value of net assets available for plan benefits at end of year		0.0	0.0
Pension Plans, Defined Benefit [Member] | Common shares of Company stock [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of net assets available for plan benefits at beginning of year		0.0
Fair value of net assets available for plan benefits at end of year		0.0	0.0
Pension Plans, Defined Benefit [Member] | Equity securities, other [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of net assets available for plan benefits at beginning of year		272.0
Fair value of net assets available for plan benefits at end of year		$ 330.7	$ 272.0
Total investments		71.20%	67.70%
Pension Plans, Defined Benefit [Member] | Equity securities, other [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of net assets available for plan benefits at beginning of year		$ 272.0
Fair value of net assets available for plan benefits at end of year		330.7	$ 272.0
Pension Plans, Defined Benefit [Member] | Equity securities, other [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of net assets available for plan benefits at beginning of year		0.0
Fair value of net assets available for plan benefits at end of year		0.0	0.0
Pension Plans, Defined Benefit [Member] | Equity securities, other [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of net assets available for plan benefits at beginning of year		0.0
Fair value of net assets available for plan benefits at end of year		0.0	0.0
Pension Plans, Defined Benefit [Member] | Equity Securities [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of net assets available for plan benefits at beginning of year		330.2
Fair value of net assets available for plan benefits at end of year		$ 394.0	$ 330.2
Total investments		84.10%	81.20%
Pension Plans, Defined Benefit [Member] | Equity Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of net assets available for plan benefits at beginning of year		$ 330.2
Fair value of net assets available for plan benefits at end of year		394.0	$ 330.2
Pension Plans, Defined Benefit [Member] | Equity Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of net assets available for plan benefits at beginning of year		0.0
Fair value of net assets available for plan benefits at end of year		0.0	0.0
Pension Plans, Defined Benefit [Member] | Equity Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of net assets available for plan benefits at beginning of year		0.0
Fair value of net assets available for plan benefits at end of year		0.0	0.0
Pension Plans, Defined Benefit [Member] | Fixed maturity securities [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of net assets available for plan benefits at beginning of year		67.3
Fair value of net assets available for plan benefits at end of year		$ 61.1	$ 67.3
Total investments		12.40%	15.60%
Pension Plans, Defined Benefit [Member] | Fixed maturity securities [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of net assets available for plan benefits at beginning of year		$ 4.0
Fair value of net assets available for plan benefits at end of year		4.1	$ 4.0
Pension Plans, Defined Benefit [Member] | Fixed maturity securities [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of net assets available for plan benefits at beginning of year		63.2
Fair value of net assets available for plan benefits at end of year		57.0	63.2
Pension Plans, Defined Benefit [Member] | Fixed maturity securities [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of net assets available for plan benefits at beginning of year		0.0
Fair value of net assets available for plan benefits at end of year		0.0	0.0
Pension Plans, Defined Benefit [Member] | Benefit plan assets, Other [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of net assets available for plan benefits at beginning of year		12.3
Fair value of net assets available for plan benefits at end of year		$ 15.9	$ 12.3
Total investments		3.50%	3.20%
Pension Plans, Defined Benefit [Member] | Benefit plan assets, Other [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of net assets available for plan benefits at beginning of year		$ 8.4
Fair value of net assets available for plan benefits at end of year		8.6	$ 8.4
Pension Plans, Defined Benefit [Member] | Benefit plan assets, Other [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of net assets available for plan benefits at beginning of year		0.0
Fair value of net assets available for plan benefits at end of year		0.0	0.0
Pension Plans, Defined Benefit [Member] | Benefit plan assets, Other [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of net assets available for plan benefits at beginning of year		3.9
Fair value of net assets available for plan benefits at end of year		$ 7.2	$ 3.9
Common Stock [Member]
Defined Benefit Plan Disclosure [Line Items]
stock acquired during period shares employee stock ownership plan | shares	2,200,000		2,383,625
Minimum [Member] | Pension Plans, Defined Benefit [Member] | Equity Securities [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Investment Policy Asset Allocation % Range Target		40.00%
Minimum [Member] | Pension Plans, Defined Benefit [Member] | Fixed maturity securities [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Investment Policy Asset Allocation % Range Target		15.00%
Minimum [Member] | Pension Plans, Defined Benefit [Member] | Benefit plan assets, Other [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Investment Policy Asset Allocation % Range Target		1.00%
Maximum [Member] | Pension Plans, Defined Benefit [Member] | Equity Securities [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Investment Policy Asset Allocation % Range Target		80.00%
Maximum [Member] | Pension Plans, Defined Benefit [Member] | Fixed maturity securities [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Investment Policy Asset Allocation % Range Target		60.00%
Maximum [Member] | Pension Plans, Defined Benefit [Member] | Benefit plan assets, Other [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Investment Policy Asset Allocation % Range Target		10.00%