Retirement Benefits (Obligations and Funded Status) (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Change in benefit obligation:
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement	$ 0	$ 0
Change in plan assets:
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement	0	0
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Service Cost	0	0
Change in benefit obligation:
Defined Benefit Plan, Interest Cost	1	2
Amounts recognized in the consolidated balance sheets consist of:
Defined Benefit Plan, Amounts for Asset (Liability) Recognized in Statement of Financial Position		0
Amounts recognized in accumulated other comprehensive loss (pre-tax basis) consist of:
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, after Tax		0
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Service Cost	1	0
Change in benefit obligation:
Defined Benefit Plan, Benefit Obligation	156	166
Defined Benefit Plan, Interest Cost	5	4
Defined Benefit Plan, Benefit Obligation, Increase (Decrease) for Plan Amendment	60	7
Defined Benefit Plan, Benefits Paid (Deprecated 2017-01-31)	(17)	(20)
Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss)	(7)	(1)
Defined Benefit Plan, Benefit Obligation	198	156
Change in plan assets:
Defined Benefit Plan, Plan Assets, Amount	257	256
Defined Benefit Plan, Plan Assets, Increase (Decrease) for Actual Return (Loss)	(8)	11
Defined Benefit Plan, Plan Assets, Contributions by Employer	9	10
Defined Benefit Plan, Plan Assets, Amount	241	257
Defined Benefit Plan, Funded (Unfunded) Status of Plan	(43)	(101)
Amounts recognized in the consolidated balance sheets consist of:
Assets for Plan Benefits, Defined Benefit Plan	68	127
Liability, Defined Benefit Plan, Current	(2)	(2)
Liability, Defined Benefit Plan, Noncurrent	(23)	(24)
Defined Benefit Plan, Amounts for Asset (Liability) Recognized in Statement of Financial Position	43	101
Amounts recognized in accumulated other comprehensive loss (pre-tax basis) consist of:
Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), after Reclassification Adjustment, before Tax	(7)	(18)
Other Comprehensive (Income) Loss, Defined Benefit Plan, Prior Service Cost (Credit), before Tax	66	21
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, after Tax	59	3
Defined Benefit Plan, Plan Assets, Benefits Paid	17	20
Funded Plans [Member]
Change in benefit obligation:
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement	0
Change in plan assets:
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement	0
Funded Plans [Member] \| Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Service Cost	0
Change in benefit obligation:
Defined Benefit Plan, Benefit Obligation	1	18
Defined Benefit Plan, Interest Cost	0	1
Defined Benefit Plan, Benefit Obligation, Increase (Decrease) for Plan Amendment	0	0
Defined Benefit Plan, Benefits Paid (Deprecated 2017-01-31)	0	(2)
Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss)	0	2
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement		(18)
Defined Benefit Plan, Benefit Obligation	1	1
Change in plan assets:
Defined Benefit Plan, Plan Assets, Amount	1	12
Defined Benefit Plan, Plan Assets, Increase (Decrease) for Actual Return (Loss)	0	3
Defined Benefit Plan, Plan Assets, Contributions by Employer	0	6
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement		(18)
Defined Benefit Plan, Plan Assets, Amount	1	1
Defined Benefit Plan, Funded (Unfunded) Status of Plan	0	0
Amounts recognized in the consolidated balance sheets consist of:
Assets for Plan Benefits, Defined Benefit Plan	0	0
Liability, Defined Benefit Plan, Current	0	0
Liability, Defined Benefit Plan, Noncurrent	0	0
Defined Benefit Plan, Amounts for Asset (Liability) Recognized in Statement of Financial Position	0
Amounts recognized in accumulated other comprehensive loss (pre-tax basis) consist of:
Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), after Reclassification Adjustment, before Tax	0	0
Other Comprehensive (Income) Loss, Defined Benefit Plan, Prior Service Cost (Credit), before Tax	0	0
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, after Tax	0
Defined Benefit Plan, Plan Assets, Benefits Paid	0	2
Unfunded Plans [Member]
Change in benefit obligation:
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement	0	0
Change in plan assets:
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement	0	0
Unfunded Plans [Member] \| Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Service Cost	0	0
Change in benefit obligation:
Defined Benefit Plan, Benefit Obligation	47	51
Defined Benefit Plan, Interest Cost	1	1
Defined Benefit Plan, Benefit Obligation, Increase (Decrease) for Plan Amendment	0	0
Defined Benefit Plan, Benefits Paid (Deprecated 2017-01-31)	(7)	(6)
Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss)	(4)	1
Defined Benefit Plan, Benefit Obligation	37	47
Change in plan assets:
Defined Benefit Plan, Plan Assets, Amount	0	0
Defined Benefit Plan, Plan Assets, Increase (Decrease) for Actual Return (Loss)	0	0
Defined Benefit Plan, Plan Assets, Contributions by Employer	0	0
Defined Benefit Plan, Plan Assets, Amount	0	0
Defined Benefit Plan, Funded (Unfunded) Status of Plan	37	47
Amounts recognized in the consolidated balance sheets consist of:
Assets for Plan Benefits, Defined Benefit Plan	0	0
Liability, Defined Benefit Plan, Current	(6)	(8)
Liability, Defined Benefit Plan, Noncurrent	(31)	(39)
Defined Benefit Plan, Amounts for Asset (Liability) Recognized in Statement of Financial Position	(37)	(47)
Amounts recognized in accumulated other comprehensive loss (pre-tax basis) consist of:
Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), after Reclassification Adjustment, before Tax	1	5
Other Comprehensive (Income) Loss, Defined Benefit Plan, Prior Service Cost (Credit), before Tax	0	0
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, after Tax	1	5
Defined Benefit Plan, Plan Assets, Benefits Paid	$ 0	$ 0

Amount of increase (decrease) in plan assets of defined benefit plan from actual return (loss) determined by change in fair value of plan assets adjusted for contributions, benefit payments, and other expenses.

Name:	us-gaap_DefinedBenefitPlanActualReturnOnPlanAssets
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of gain (loss) from change in actuarial assumptions which (increases) decreases benefit obligation of defined benefit plan. Assumptions include, but are not limited to, interest, mortality, employee turnover, salary, and temporary deviation from substantive plan.