Shareholders' Equity (Summary Of Changes In Accumulated Other Comprehensive Income (Loss)) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accumulated other comprehensive income [Line Items]
Accumulated Other Comprehensive Income (Loss), Net of Tax	$ (250)				$ (139)				$ (250)	$ (139)	$ (122)
Other Comprehensive Income (Loss), Securities, Available-for-Sale, Unrealized Holding Gain (Loss) Arising During Period, Tax									(37)	19
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Tax									1	(1)
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, Tax									0	11
Other Comprehensive Income (Loss), Tax									(36)	29
Other Comprehensive Income (Loss), Net of Tax									(111)	(17)	(67)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax									(116)	6
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax									5	2
Effect of Change in Tax Rate, Shareholders' Equity										(25)
Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Amount									2	(47)	0
Effect of Change in Tax Rate, OCI									0	25	0
Income Tax Expense (Benefit)									259	344	236
Net Income (Loss) Available to Common Stockholders, Basic	217	$ 215	$ 187	$ 231	114	$ 153	$ 154	$ 129	850	550	411
Reclassification of amortization of net actuarial gains losses pension and post retirement from AOCI, gross									(3)	(7)	(8)
Reclassification of pension and postretirement from accumulated other comprehensive income, tax									(1)	(3)	(3)
Accumulated Net Unrealized Investment Gain (Loss) [Member]
Accumulated other comprehensive income [Line Items]
Accumulated Other Comprehensive Income (Loss), Net of Tax	(228)				(114)				(228)	(114)	(92)
Other Comprehensive Income (Loss), Net of Tax									(114)	(22)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax									(114)	(2)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax									0	0
Effect of Change in Tax Rate, Shareholders' Equity										(20)
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]
Accumulated other comprehensive income [Line Items]
Accumulated Other Comprehensive Income (Loss), Net of Tax	(1)				(3)				(1)	(3)	1
Other Comprehensive Income (Loss), Net of Tax									2	(4)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax									(1)	(1)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax									3	(2)
Effect of Change in Tax Rate, Shareholders' Equity										(1)
Net Income (Loss) Available to Common Stockholders, Basic									(3)	2	7
Accumulated Defined Benefit Plans Adjustment [Member]
Accumulated other comprehensive income [Line Items]
Accumulated Other Comprehensive Income (Loss), Net of Tax	$ (21)				$ (22)				(21)	(22)	(31)
Other Comprehensive Income (Loss), Net of Tax									1	9
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax									(1)	9
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax									2	4	5
Effect of Change in Tax Rate, Shareholders' Equity										(4)
Interest Rate Contract [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]
Accumulated other comprehensive income [Line Items]
Gain (Loss) on Derivative Instruments, Net, Pretax									(4)	4	11
Income Tax Expense (Benefit)									$ (1)	$ 2	$ 4