Pension Benefits (Summary Of Pension Plan Assets Using Fair Value Hierarchy By Asset Class) (Details) (Defined Pension Benefit Plans [Member], USD $) In Millions, unless otherwise specified	Mar. 31, 2012		Mar. 31, 2011		Mar. 31, 2010
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	$ 410		$ 416		$ 391
Cash And Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	28		45
Common Stock [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	100
Common And Preferred Stock [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets			105
Equity Commingled Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	134		144
Government Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	11		20
Corporate Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	48		26
Mortgage-Backed Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	21		28
Asset-Backed Securities And Other [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	20		19
Fixed Income Commingled Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	25		34
Other Commingled Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	12
Real Estate Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	17		5
Hedge Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets			5
Total [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	416		431
Receivables [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	6	[1]	19	[2]
Payables [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	(12)	[1]	(34)	[2]
Fair Value, Inputs, Level 1 [Member] | Cash And Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	14		14
Fair Value, Inputs, Level 1 [Member] | Common Stock [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	100
Fair Value, Inputs, Level 1 [Member] | Common And Preferred Stock [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets			104
Fair Value, Inputs, Level 1 [Member] | Equity Commingled Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	0		0
Fair Value, Inputs, Level 1 [Member] | Government Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	0		0
Fair Value, Inputs, Level 1 [Member] | Corporate Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	0		0
Fair Value, Inputs, Level 1 [Member] | Mortgage-Backed Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	0		0
Fair Value, Inputs, Level 1 [Member] | Asset-Backed Securities And Other [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	0		0
Fair Value, Inputs, Level 1 [Member] | Fixed Income Commingled Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	0		0
Fair Value, Inputs, Level 1 [Member] | Other Commingled Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	0
Fair Value, Inputs, Level 1 [Member] | Real Estate Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	0		0
Fair Value, Inputs, Level 1 [Member] | Hedge Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets			0
Fair Value, Inputs, Level 1 [Member] | Total [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	114		118
Fair Value, Inputs, Level 2 [Member] | Cash And Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	14		31
Fair Value, Inputs, Level 2 [Member] | Common Stock [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	0
Fair Value, Inputs, Level 2 [Member] | Common And Preferred Stock [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets			1
Fair Value, Inputs, Level 2 [Member] | Equity Commingled Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	134		144
Fair Value, Inputs, Level 2 [Member] | Government Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	11		20
Fair Value, Inputs, Level 2 [Member] | Corporate Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	48		26
Fair Value, Inputs, Level 2 [Member] | Mortgage-Backed Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	21		28
Fair Value, Inputs, Level 2 [Member] | Asset-Backed Securities And Other [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	20		19
Fair Value, Inputs, Level 2 [Member] | Fixed Income Commingled Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	25		34
Fair Value, Inputs, Level 2 [Member] | Other Commingled Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	12
Fair Value, Inputs, Level 2 [Member] | Real Estate Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	0		0
Fair Value, Inputs, Level 2 [Member] | Hedge Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets			0
Fair Value, Inputs, Level 2 [Member] | Total [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	285		303
Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	17		10		26
Level 3 [Member] | Cash And Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	0		0
Level 3 [Member] | Common Stock [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	0
Level 3 [Member] | Common And Preferred Stock [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets			0
Level 3 [Member] | Equity Commingled Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	0		0
Level 3 [Member] | Government Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	0		0
Level 3 [Member] | Corporate Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	0		0
Level 3 [Member] | Mortgage-Backed Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	0		0
Level 3 [Member] | Asset-Backed Securities And Other [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	0		0
Level 3 [Member] | Fixed Income Commingled Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	0		0
Level 3 [Member] | Other Commingled Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	0
Level 3 [Member] | Real Estate Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	17		5		19
Level 3 [Member] | Hedge Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	0		5		5
Level 3 [Member] | Total [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	$ 17		$ 10

[1] Represents pending trades at March 31, 2012.

[2] Represents pending trades at March 31, 2011.