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, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Employee Retirement Benefits [Abstract]
Service cost	$ 12	$ 11	$ 10
Interest cost	14	14	14
Expected return on plan assets	(16)	(16)	(14)
Amortization of actuarial loss and prior service cost	8	4	2
Net periodic benefit cost	18	13	12
Current year actuarial loss	20	30	0
Recognition of actuarial loss	(6)	(4)	(2)
Recognition of prior service cost	(1)	(1)	(1)
Total loss (gain) recognized in other comprehensive income	$ 13	$ 25	$ (3)