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Commitments and Contingencies, Technology Agreements (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
IBM Agreement [Member]
Technology Agreements [Abstract]
Technology Agreement Expiration Date		2022
Percent of contract value to be paid if contract is terminated (in hundredths)		50.00%
Technology Agreements, Minimum Payments Due [Abstract]
2019	$ 30
2020	16
2021	16
2022	7
2023	0
Thereafter	0
Information Technology and Data Processing	81	$ 98	$ 119
Accenture Agreement [Member]
Technology Agreements [Abstract]
Technology Agreement Expiration Date		2020
Technology Agreements, Minimum Payments Due [Abstract]
2019	11
2020	11
2021	0
2022	0
2023	0
Thereafter	0
Information Technology and Data Processing	$ 46	$ 16	$ 35

X

- Definition

The amount of expenses incurred in the period for information technology and data processing products and services.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.6)
-URI http://asc.fasb.org/extlink&oid=115205541&loc=SL114868664-224227

+ Details

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

X

- Definition

-- None. No documentation exists for this element. --

+ References

No definition available.

+ Details

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X

- Definition

For technology service agreements having initial or remaining terms in excess of one year, required payments due after the fifth year of the balance sheet date.

+ References

No definition available.

+ Details

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Namespace Prefix:	xel_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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X

- Definition

For technology service agreements having initial or remaining terms in excess of one year, required payments due within one year of the balance sheet date.

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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- Definition

For technology service agreements having initial or remaining terms in excess of one year, required payments due within the fourth year of the balance sheet date.

+ References

No definition available.

+ Details

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Balance Type:	credit
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X

- Definition

For technology service agreements having initial or remaining terms in excess of one year, required payments due within the third year of the balance sheet date.

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

X

- Definition

For technology service agreements having initial or remaining terms in excess of one year, required payments due within the second year of the balance sheet date.

+ References

No definition available.

+ Details

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Namespace Prefix:	xel_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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X

- Definition

Percent of contract value to be paid if contract is cancelled by entity.

+ References

No definition available.

+ Details

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Namespace Prefix:	xel_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Technology Agreement Expiration

+ References

No definition available.

+ Details

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Balance Type:	na
Period Type:	duration

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- Definition

-- None. No documentation exists for this element. --

+ References

No definition available.

+ Details

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X

- Definition

For technology service agreements having initial or remaining terms in excess of one year, required payments due within the fourth year of the balance sheet date.

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
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- Details

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- Details

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