Comprehensive Income (Loss) (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Comprehensive Income (Loss) [Abstract]
Defined Benefit Plan, Benefit Obligation, (Increase) Decrease for Remeasurement due to Settlement		$ 7	$ 32
Other comprehensive income, Recognition of net actuarial loss for pension settlement costs, before tax	$ 15	34	$ 77
Pension settlement costs, net of tax		$ 26

Amount, after tax, of increase (decrease) to other comprehensive income from settlement and curtailment gain (loss) of defined benefit plan.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
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-Section 50
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
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-Name Accounting Standards Codification
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Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
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-Name Accounting Standards Codification
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