Accumulated Other Comprehensive Loss (Reconciliation Of The Components Of Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Comprehensive Income (Loss), Net of Tax, Attributable to Parent [Abstract]
Investments, Accumulated Gross Unrealized Gain, before Tax	$ 986	$ 1,136
Investments, Accumulated Gross Unrealized Loss, before Tax	(107)	(245)
Investments, Accumulated Gross Unrealized Gain (Loss), before Tax	879	891
Deferred tax (liability) asset	(210)	(216)
Investments, Accumulated Adjustment for Noncontrolling Interest	(3)	0
Investments, Accumulated Net Unrealized Gains (Losses), after Tax	666	675
Accumulated other comprehensive income (loss), non-credit component of impairments on investments	(1)	(11)
Non-Credit Component of Impairments on Investments In Accumulated Other Comprehensive Income Deferred Tax Liability Asset	0	3
Accumulated Other Comprehensive Income Loss Non-Credit Component of Impairment Loss on Investments Net Of Tax	(1)	(8)
Unrealized Gain (Loss) on Interest Rate Cash Flow Hedges, Pretax, Accumulated Other Comprehensive Income (Loss)	(304)	(319)
Cash flow hedges, deferred tax asset	64	67
AOCI, Cash Flow Hedge, Cumulative Gain (Loss), after Tax	(240)	(252)
Defined benefit pension plans, deferred net actuarial loss	(710)	(695)
Defined benefit pension plans, deferred prior service credits	0	(1)
Defined benefit pension plans, deferred tax asset	180	178
Defined Benefit Plan Accumulated Other Comprehensive Income Adjustments Net Of Tax	(530)	(518)
Postretirement benefit plans, deferred net actuarial loss	(3)	(25)
Deferred Prior Service Cost (Credit) Postretirement Benefit Plans	9	14
Deferred Tax Liability, Postretirement Benefits	(2)
Postretirement benefit plans, deferred tax asset		3
Net unrecognized periodic benefit credit (costs) for postretirement benefit plans	4	(8)
Foreign currency translation adjustments, gross unrealized losses	(3)	(1)
Foreign currency translation adjustments, deferred tax asset	1	0
Accumulated Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Net of Tax	(2)	(1)
Accumulated other comprehensive loss	$ (103)	$ (112)	$ 150