Retirement Plans (Fair Value Measurements Using Significant Unobservable Inputs (Level 3)) (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Other Fixed Income [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, January 1	$ (802)
Fair value of plan assets, December 31	(723)	$ (802)
Derivatives [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, January 1	8
Fair value of plan assets, December 31	98	8
Mortgage Backed Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, January 1	1
Fair value of plan assets, December 31	0	1
Domestic Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, January 1	11,368	10,312
Fair value of plan assets, December 31	8,735	11,368
Domestic Plan [Member] \| Significant Unobservable Inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, January 1	29	(59)
Relating to assets still held at the reporting date	76	95
Relating to assets sold during the period	(19)	(23)
Purchases, sales and settlements	25	16
Transfers in and/or out of Level 3	0	0
Fair value of plan assets, December 31	111	29
Domestic Plan [Member] \| Other Fixed Income [Member] \| Significant Unobservable Inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, January 1	12	11
Relating to assets still held at the reporting date	1	1
Relating to assets sold during the period	0	0
Purchases, sales and settlements	0	0
Transfers in and/or out of Level 3	0	0
Fair value of plan assets, December 31	13	12
Domestic Plan [Member] \| Derivatives [Member] \| Significant Unobservable Inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, January 1	16	(71)
Relating to assets still held at the reporting date	75	94
Relating to assets sold during the period	(19)	(23)
Purchases, sales and settlements	26	16
Transfers in and/or out of Level 3	0	0
Fair value of plan assets, December 31	98	16
Domestic Plan [Member] \| Mortgage Backed Securities [Member] \| Significant Unobservable Inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, January 1	1	1
Relating to assets still held at the reporting date	0	0
Relating to assets sold during the period	0	0
Purchases, sales and settlements	(1)	0
Transfers in and/or out of Level 3	0	0
Fair value of plan assets, December 31	$ 0	$ 1

Amount, measured using unobservable inputs, of increase (decrease) in plan assets of defined benefit plan from actual return (loss) on assets sold.

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- Definition

Amount, measured using unobservable inputs, of increase (decrease) in plan assets of defined benefit plan from actual return (loss) on assets still held.

+ References

+ Details

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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- Definition

Amount of asset segregated and restricted to provide benefit under defined benefit plan. Asset includes, but is not limited to, stock, bond, other investment, earning from investment, and contribution by employer and employee.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
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+ Details

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- Definition

Amount, measured using unobservable input, of increase (decrease) in plan asset of defined benefit plan from purchase, sale and settlement of trade associated with underlying investment.

+ References

+ Details

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- Definition

Amount, measured using unobservable inputs, of increase (decrease) in plan assets of defined benefit plan, for assets transferred into (out of) Level 3 of fair value hierarchy. Includes, but is not limited to, transfer due to change in observability of significant inputs.

+ References

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