Other Comprehensive Income (Loss) (Components of Other Comprehensive Income Loss) (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	$ 7,442	$ 6,272
Other comprehensive (loss) income, net of tax	(590)	1,050	$ (873)
Ending balance	7,584	7,442	6,272
Foreign currency translation adjustments, tax portion	15	(11)
Net unrealized investment gains, tax portion		7
Net charges related to pension/ retiree plans, tax portion	(1,493)	(1,462)
Unrealized Investment Gains
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	14	19
Cumulative effect of amended accounting standard	(14)
Other comprehensive (loss) before reclassifications	0	(5)
Amounts reclassified from accumulated other comprehensive loss	0	0
Other comprehensive (loss) income, net of tax	0	(5)
Ending balance	0	14	19
Pension/Post-Retirement Plans Gains (Losses)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	(2,892)	(3,232)
Cumulative effect of amended accounting standard	0
Other comprehensive (loss) before reclassifications	(205)	160
Amounts reclassified from accumulated other comprehensive loss	144	180
Other comprehensive (loss) income, net of tax	(61)	340
Ending balance	(2,953)	(2,892)	(3,232)
Foreign Currency Translation Adjustments
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	(1,165)	(1,880)
Cumulative effect of amended accounting standard	0
Other comprehensive (loss) before reclassifications	(529)	715
Amounts reclassified from accumulated other comprehensive loss	0	0
Other comprehensive (loss) income, net of tax	(529)	715
Ending balance	(1,694)	(1,165)	(1,880)
Accumulated Other Comprehensive Loss
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	(4,043)	(5,093)	(4,220)
Cumulative effect of amended accounting standard	(14)
Other comprehensive (loss) before reclassifications	(734)	870
Amounts reclassified from accumulated other comprehensive loss	144	180
Other comprehensive (loss) income, net of tax	(590)	1,050	(873)
Ending balance	$ (4,647)	$ (4,043)	$ (5,093)

Accumulated Other Comprehensive Income (Loss), Available-For-Sale Securities, Adjustment, Tax

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Accumulated Other Comprehensive Income (Loss), Defined Benefit Pension And Other Postretirement Plans, Adjustment, Tax

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Amount after tax, before reclassification adjustments of other comprehensive income (loss).

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Amount of stockholders' equity (deficit), net of receivables from officers, directors, owners, and affiliates of the entity, attributable to both the parent and noncontrolling interests. Amount excludes temporary equity. Alternate caption for the concept is permanent equity.

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