Retirement And Other Employee Benefits (Summary Of Pension Benefits And Retirement Health Benefits Plans) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Pension Benefits
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Projected benefit obligation at beginning of year	$ (752.2)	$ (823.1)
Interest cost	(28.6)	(26.3)	$ (26.3)
Actuarial (loss) gain, including curtailments and settlements	(99.5)	46.9
Benefits paid	55.2	50.3
Projected benefit obligation at end of year	(825.1)	(752.2)	(823.1)
Change in plan assets
Fair value of plan assets at beginning of year	732.3	807.1
Actual return (loss) on plan assets	119.7	(32.5)
Employer contributions	13.7	9.2
Benefits paid (including administrative expenses)	(56.7)	(51.5)
Fair value of plan assets at end of year	809.0	732.3	807.1
Funded status at end of year	(16.1)	(19.9)
Retirement Health Benefits
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Projected benefit obligation at beginning of year	(94.5)	(104.0)
Interest cost	(3.1)	(3.3)	(3.4)
Actuarial (loss) gain, including curtailments and settlements	7.5	7.7
Benefits paid	4.7	5.1
Projected benefit obligation at end of year	(85.4)	(94.5)	(104.0)
Change in plan assets
Fair value of plan assets at beginning of year	41.9	48.8
Actual return (loss) on plan assets	6.6	(2.0)
Employer contributions	0.2	0.2
Benefits paid (including administrative expenses)	(4.7)	(5.1)
Fair value of plan assets at end of year	44.0	41.9	$ 48.8
Funded status at end of year	$ (41.4)	$ (52.6)