Summary Of Significant Accounting Policies Summary of Significant Accounting Policies (Summary of Nonvested Shares Related To Long-Term Incentive Plan) (Details) - $ / shares		3 Months Ended
		Mar. 31, 2017	Dec. 31, 2016
Weighted-average Fair Value per Unit at Grant Date
Closing common share price			$ 52.46
Performance Shares
Share Units
Share Units, Nonvested as of beginning of year		1,059,639
Share Units, Granted	[1]	496,068
Share Units, Forfeitures		(3,192)
Share Units, Vested	[2]	(3,779)
Share Units, Nonvested as of Current period end		1,548,736
Weighted-average Fair Value per Unit at Grant Date
Weighted-average Fair Value per Unit, Nonvested as of Beginning of year		$ 48.04
Weighted-average Fair Value per Unit, Grants	[1]	59.16
Weighted-average Fair Value per Unit, Forfeitures		49.13
Weighted-average Fair Value per Unit, Vested	[2]	52.88
Weighted-average Fair Value per Unit, Nonvested as of Current period end		$ 51.59
Performance period		3 years
Risk free interest rate period		3 years
Three-year risk-free rate		1.47%
Volatility rate, minimum		15.00%
Volatility rate, maximum		21.00%

[1] Performance share units granted to certain executive and nonexecutive officers and other eligible employees under the 2014 Incentive Plan.

[2] (b)Performance share units vested due to the attainment of retirement eligibility by certain employees. Actual shares issued for retirement-eligible employees vary depending on actual performance over the three-year measurement period.