Capital Stock (Stock Option, SARs, Restricted Stock and Restricted Share Unit Activity) (Details) shares in Millions	6 Months Ended
Sep. 30, 2023 $ / shares shares
Class A Voting Shares \| Stock Options and SARs
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Outstanding at March 31, 2023 (in shares)	4.3
Granted (in shares)	0.0
Options exercised (in shares)	0.0
Forfeited or expired (in shares)	(1.8)
Outstanding at September 30. 2023 (in shares)	2.5
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Outstanding at March 31, 2023, weighted average exercise price (in usd per share) \| $ / shares	$ 26.35
Granted, weighted average exercise price (in usd per share) \| $ / shares	0
Options exercised, weighted average exercise price (in usd per share) \| $ / shares	7.70
Forfeited or expired, weighted average exercise price (in usd per share) \| $ / shares	30.79
Outstanding at September 30, 2023, weighted average exercise price (in usd per share) \| $ / shares	$ 22.99
Class A Voting Shares \| Restricted Stock and Restricted Share Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Outstanding at March 31, 2023 (in shares)	0.0
Granted (in shares)	0.0
Vested (in shares)	0.0
Forfeited or expired (in shares)	0.0
Outstanding at September 30, 2023 (in shares)	0.0
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Outstanding at March 31, 2023, weighted average grant-date fair value (in usd per share) \| $ / shares	$ 10.95
Granted, weighted average grant date fair value (in usd per share) \| $ / shares	0
Restricted stock or RSUs vested, weighted average grant-date fair value (in usd per share) \| $ / shares	10.89
Forfeited or expired, weighted average grant-date fair value (in usd per share) \| $ / shares	0
Outstanding at September 30, 2023, weighted average grant-date fair value (in usd per share) \| $ / shares	$ 11.01
Class B Non-Voting Shares \| Stock Options and SARs
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Outstanding at March 31, 2023 (in shares)	20.5
Granted (in shares)	0.0
Options exercised (in shares)	(0.1)
Forfeited or expired (in shares)	(2.1)
Outstanding at September 30. 2023 (in shares)	18.3
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Outstanding at March 31, 2023, weighted average exercise price (in usd per share) \| $ / shares	$ 15.23
Granted, weighted average exercise price (in usd per share) \| $ / shares	0
Options exercised, weighted average exercise price (in usd per share) \| $ / shares	7.15
Forfeited or expired, weighted average exercise price (in usd per share) \| $ / shares	29.19
Outstanding at September 30, 2023, weighted average exercise price (in usd per share) \| $ / shares	$ 13.82
Class B Non-Voting Shares \| Restricted Stock and Restricted Share Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Outstanding at March 31, 2023 (in shares)	14.0
Granted (in shares)	9.2
Vested (in shares)	(9.1)
Forfeited or expired (in shares)	(0.5)
Outstanding at September 30, 2023 (in shares)	13.6
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Outstanding at March 31, 2023, weighted average grant-date fair value (in usd per share) \| $ / shares	$ 9.48
Granted, weighted average grant date fair value (in usd per share) \| $ / shares	8.19
Restricted stock or RSUs vested, weighted average grant-date fair value (in usd per share) \| $ / shares	9.33
Forfeited or expired, weighted average grant-date fair value (in usd per share) \| $ / shares	8.77
Outstanding at September 30, 2023, weighted average grant-date fair value (in usd per share) \| $ / shares	$ 8.73
Maximum \| Class A Voting Shares \| Stock Options and SARs
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Options exercised (in shares)	(0.1)
Forfeited or expired (in shares)	(0.1)
Maximum \| Class A Voting Shares \| Restricted Stock and Restricted Share Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Outstanding at March 31, 2023 (in shares)	0.1
Outstanding at September 30, 2023 (in shares)	0.1
Maximum \| Class B Non-Voting Shares \| Stock Options and SARs
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Granted (in shares)	0.1

The number of equity-based payment instruments, excluding stock (or unit) options, that were forfeited during the reporting period.

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Weighted average fair value as of the grant date of equity-based award plans other than stock (unit) option plans that were not exercised or put into effect as a result of the occurrence of a terminating event.

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The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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- Definition

The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(i)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

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-Topic 718
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-Paragraph 2
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-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

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Per share or unit weighted-average fair value of nonvested award under share-based payment arrangement. Excludes share and unit options.

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The number of equity-based payment instruments, excluding stock (or unit) options, that vested during the reporting period.

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- Definition

The weighted average fair value as of grant date pertaining to an equity-based award plan other than a stock (or unit) option plan for which the grantee gained the right during the reporting period, by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash in accordance with the terms of the arrangement.

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- Definition

For presentations that combine terminations, the number of shares under options that were cancelled during the reporting period as a result of occurrence of a terminating event specified in contractual agreements pertaining to the stock option plan or that expired.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(iv)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

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Weighted average price of options that were either forfeited or expired.

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Gross number of share options (or share units) granted during the period.

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- Definition

Number of options outstanding, including both vested and non-vested options.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(i)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

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- Definition

Weighted average price at which grantees can acquire the shares reserved for issuance under the stock option plan.

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- Definition

Weighted average price at which option holders acquired shares when converting their stock options into shares.

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Weighted average per share amount at which grantees can acquire shares of common stock by exercise of options.

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Number of share options (or share units) exercised during the current period.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-SubTopic 10
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
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Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 210
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