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Retirement Plans (Plan's Allocated Target Ranges and Actual Weighted Average Asset Allocation by Investment Categories) (Details) - USD ($) $ in Millions | 12 Months Ended |
--- | --- | ---
Dec. 31, 2018 | Dec. 31, 2017
Plan Assets Redeployed into Risk Seeking Investments |  | $ 49 |
Actual percentage |  | 100.00% | 100.00%
Percent of Plan Assets Redeployed into Risk Seeking Investments |  | 15.00% |
Percent Hedge Against Projected Benefit Obligation |  | 50.00% |
Return Seeking Assets [Member] |  |  |
Actual percentage |  | 43.00% | 58.00%
Liability Hedging Assets [Member] |  |  |
Actual percentage |  | 38.00% | 40.00%
Short-term Investments Excluding Redeployment[Member] |  |  |
Actual percentage | [1] | 5.00% |
Short-term Investments [Member] |  |  |
Actual percentage | [1] | 19.00% | 2.00%
Minimum [Member] | Return Seeking Assets [Member] |  |  |
Defined Benefit Plan, Plan Assets, Investment Policy and Strategy, Description |  | 0.15 |
Minimum [Member] | Liability Hedging Assets [Member] |  |  |
Defined Benefit Plan, Plan Assets, Investment Policy and Strategy, Description |  | 0.35 |
Minimum [Member] | Short-term Investments [Member] |  |  |
Defined Benefit Plan, Plan Assets, Investment Policy and Strategy, Description |  | 0 |
Maximum [Member] | Return Seeking Assets [Member] |  |  |
Defined Benefit Plan, Plan Assets, Investment Policy and Strategy, Description |  | 0.7 |
Maximum [Member] | Liability Hedging Assets [Member] |  |  |
Defined Benefit Plan, Plan Assets, Investment Policy and Strategy, Description |  | 0.75 |
Maximum [Member] | Short-term Investments [Member] |  |  |
Defined Benefit Plan, Plan Assets, Investment Policy and Strategy, Description |  | 0.02 |
[1] | The actual percentage of assets allocated to short-term investments is higher than our target as of December 31, 2018 due to portfolio rebalancing initiatives that are expected to be completed during 2019. As part of this rebalancing initiative, $49 million, or 15%, of plan assets were redeployed into risk seeking assets in January 2019. Excluding the impact of this redeployment, our short-term investments represented 5% of plan assets at December 31, 2018.

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- Definition Description of investment policy and strategy for defined benefit plan asset. Includes, but is not limited to, investment allocation decision and factor pertinent to understanding investment policy and strategy for plan asset. Factor includes, but is not limited to, investment goal, risk management practice, permitted and prohibited investment including use of derivative, diversification, and relationship between plan asset and obligation. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 55 -Paragraph 17 -URI http://asc.fasb.org/extlink&oid=112275985&loc=d3e4179-114921 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(i) -URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e1928-114920 + Details
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