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Benefit Plans (Summary Of Performance Shares and Performance Units Vested Awards) (Details) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Performance Shares Liability Awards [Member] |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Vested (in shares/awards) | 63,565 | 66,322 | 90,806
Performance Units Liability Awards [Member] |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Vested (in shares/awards) | 16,661 | 20,131 | 31,910
2017 Grant [Member] | Performance Shares Liability Awards [Member] |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Vested (in shares/awards) | 63,565 |  |
Vested percentage of the target | 155.00% |  |
Cash and stock payout value | $ 6 |  |
Cash payout value | $ 5 |  |
Common stock shares from vested performance shares (in shares) | 9,543 |  |
2017 Grant [Member] | Performance Units Liability Awards [Member] |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Vested (in shares/awards) | 16,661 |  |
Vested percentage of the target | 155.00% |  |
Cash and stock payout value | $ 2 |  |
Cash payout value | $ 2 |  |
2016 Grant [Member] | Performance Shares Liability Awards [Member] |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Vested (in shares/awards) |  | 66,322 |
Vested percentage of the target |  | 142.50% |
Cash and stock payout value |  | $ 4 |
Cash payout value |  | $ 4 |
Common stock shares from vested performance shares (in shares) |  | 6,447 |
2016 Grant [Member] | Performance Units Liability Awards [Member] |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Vested (in shares/awards) |  | 20,131 |
Vested percentage of the target |  | 142.50% |
Cash and stock payout value |  | $ 1 |
Cash payout value |  | $ 1 |
2015 Grant [Member] | Performance Shares Liability Awards [Member] |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Vested (in shares/awards) |  |  | 90,806
Vested percentage of the target |  |  | 137.50%
Cash and stock payout value |  |  | $ 5
Cash payout value |  |  | $ 5
Common stock shares from vested performance shares (in shares) |  |  | 5,078
2015 Grant [Member] | Performance Units Liability Awards [Member] |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Vested (in shares/awards) |  |  | 31,910
Vested percentage of the target |  |  | 137.50%
Cash and stock payout value |  |  | $ 1
Cash payout value |  |  | $ 1

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- Definition Aggregate cash paid by the entity during the period to settle equity instruments granted under equity-based payment arrangements. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (k) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
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- Definition The number of equity-based payment instruments, excluding stock (or unit) options, that vested during the reporting period. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(2)(iii)(2) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
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- Definition Number of shares issued under share-based payment arrangement. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
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