Accumulated Other Comprehensive Loss (Reconciliation Of The Components Of Accumulated Other Comprehensive Loss) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Gross Unrealized Gains	$ 1,316	$ 720
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	(65)	(44)
Available-for-sale Securities, Accumulated Gross Unrealized Gain (Loss), before Tax	1,251	676
Investments, deferred tax asset (liability)	(302)	(155)
Net unrealized gains on investments, after tax	949	521
Non-credit component of impairments on investments	(3)	(3)
Deferred tax asset on non-credit component of impairments on investments	1	1
Net unrealized non-credit component of impairments on investments, after tax	(2)	(2)
Cash flow hedge unrealized gain (Loss) before tax	(316)	(331)
Cash Flow Hedging Instruments Accumulated Other Comprehensive Income Net Deferred Tax Asset	66	69
Accumulated Other Comprehensive Income (Loss), Cumulative Changes in Net Gain (Loss) from Cash Flow Hedges, Effect Net of Tax	(250)	(262)
Defined Benefit Plan, Accumulated Other Comprehensive Income (Loss), Gain (Loss), before Tax	(749)	(734)
Prior service cost (credit)	0	(1)
Defined Benefit Plan Accumulated Other Comprehensive Income Net Deferred Tax Asset	190	188
Defined Benefit Plan Accumulated Other Comprehensive Income Adjustments Net Of Tax	(559)	(547)
Postretirement benefit plans, deferred net actuarial loss	(3)	(25)
Postretirement benefit plans, deferred prior service credit	12	19
Postretirement Benefits, Deferred Tax Liability	(2)
Postretirement benefit plans, Deferred tax asset		2
Accumulated Other Comprehensive (Income) Loss, Defined Benefit Plan, after Tax	7	(4)
Foreign currency translation adjustments, Gross unrealized losses	6	(3)
Foreign currency translation adjustments, Deferred tax asset		1
Foreign currency translation adjustments, deferred tax liability	(1)
Accumulated Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Net of Tax	5	(2)
Accumulated Other Comprehensive Income (Loss), Net of Tax	$ 150	$ (296)