Accumulated Other Comprehensive Loss (Reconciliation Of The Components Of Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Investments, Accumulated Gross Unrealized Gain, before Tax	$ 1,136	$ 770
Investments, Accumulated Gross Unrealized Loss, before Tax	(245)	(54)
Investments, net pretax unrealized gains (losses) excluding non-credit component of other-than-temporary impairments	891	716
Deferred tax (liability) asset	(216)	(164)
Net unrealized gains (losses) on investments excluding non-credit component of other-than-temporary impairments	675	552
Accumulated other comprehensive income (loss), non-credit component of impairments on investments	(11)	(5)
Non-Credit Component of Impairments on Investments In Accumulated Other Comprehensive Income Deferred Tax Liability Asset	3	1
Accumulated Other Comprehensive Income Loss Non-Credit Component of Impairment Loss on Investments Net Of Tax	(8)	(4)
Unrealized Gain (Loss) on Interest Rate Cash Flow Hedges, Pretax, Accumulated Other Comprehensive Income (Loss)	(319)	(340)
Cash flow hedges, deferred tax asset	67	63
AOCI, Cash Flow Hedge, Cumulative Gain (Loss), after Tax	(252)	(277)
Defined benefit pension plans, deferred net actuarial loss	(695)	(730)
Defined benefit pension plans, deferred prior service credits	(1)	(1)
Defined benefit pension plans, deferred tax asset	178	188
Net unrecognized periodic benefit costs for defined benefit pension plans	(518)	(543)
Postretirement benefit plans, deferred net actuarial loss	(25)	(57)
Postretirement beneft plans, prior service costs	14	25
Postretirement benefit plans, deferred tax asset	3	8
Net unrecognized periodic benefit costs for postretirement benefit plans	(8)	(24)
Foreign currency translation adjustments, gross unrealized losses	(1)	(4)
Foreign currency translation adjustments, deferred tax asset	0	1
Net unrealized losses on foreign currency translation adjustments	(1)	(3)
Accumulated other comprehensive loss	$ (112)	$ (299)	$ (296)