Employee Retirement Benefits (Components Of Net Periodic Benefit Cost As Well As Other Changes In Plan Assets And Benefit Obligations Recognized In Other Comprehensive Income For Qualified Plan And SERP) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Retirement Benefits [Abstract]
Service cost	$ 11	$ 11	$ 12
Interest cost	14	14	14
Expected return on plan assets	(21)	(19)	(18)
Amortization of actuarial loss and prior service cost	2	3	6
Other	1	0	1
Net periodic benefit cost	7	9	15
Current year actuarial (gain) loss	(11)	(13)	13
Amortization of actuarial loss	(3)	(2)	(6)
Amortization of prior service cost	0	(1)	(1)
Total recognized in other comprehensive (income) loss	(14)	(16)	6
Total recognized in net periodic benefit cost and other comprehensive (income) loss	$ (7)	$ (7)	$ 21