Earnings Per Common Share (Basic and Diluted Earnings per Common Share) (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended																12 Months Ended
	Mar. 31, 2014		Dec. 31, 2013		Sep. 30, 2013		Jun. 30, 2013		Mar. 31, 2013		Dec. 31, 2012		Sep. 30, 2012		Jun. 30, 2012		Mar. 31, 2014		Mar. 31, 2013		Mar. 31, 2012
Earnings Per Share, Basic and Diluted, by Common Class [Line Items]
Income from continuing operations	$ 362	[1],[2]	$ 156	[1],[2]	$ 416	[1],[2]	$ 420	[1],[2]	$ 263	[3],[4],[5]	$ 306	[3],[4],[5]	$ 399	[3],[4],[5]	$ 379	[3],[4],[5]	$ 1,354		$ 1,347		$ 1,379
Net loss attributable to noncontrolling interests	5	[6]	0	[6]	0	[6]	0	[6]	0		0		0		0		5		0		0
Income from continuing operations attributable to McKesson																	1,359		1,347		1,379
Income (Loss) from Discontinued Operations, Net of Tax	4	[7]	(92)	[7]	(12)	[7]	4	[7]	(4)		(8)		2		1		(96)		(9)		24
Net income attributable to McKesson	$ 371		$ 64		$ 404		$ 424		$ 259		$ 298		$ 401		$ 380		$ 1,263		$ 1,338		$ 1,403
Weighted average common shares outstanding:
Basic																	229		235		246
Effect of dilutive securities:
Diluted																	233		239		251
Diluted
Continuing operations	$ 1.56		$ 0.67		$ 1.79		$ 1.81		$ 1.11		$ 1.27		$ 1.66		$ 1.58		$ 5.83	[8]	$ 5.62	[8]	$ 5.49	[8]
Discontinued operations	$ 0.02		$ (0.39)		$ (0.05)		$ 0.02		$ (0.01)		$ (0.03)		$ 0.01		$ 0.00		$ (0.42)	[8]	$ (0.03)	[8]	$ 0.10	[8]
Total	$ 1.58		$ 0.28		$ 1.74		$ 1.83		$ 1.10		$ 1.24		$ 1.67		$ 1.58		$ 5.41	[8]	$ 5.59	[8]	$ 5.59	[8]
Basic
Continuing operations	$ 1.59		$ 0.68		$ 1.82		$ 1.84		$ 1.13		$ 1.30		$ 1.69		$ 1.61		$ 5.93	[8]	$ 5.74	[8]	$ 5.60	[8]
Discontinued operations	$ 0.02		$ (0.40)		$ (0.06)		$ 0.02		$ (0.01)		$ (0.03)		$ 0.01		$ 0.00		$ (0.42)	[8]	$ (0.03)	[8]	$ 0.10	[8]
Total	$ 1.61		$ 0.28		$ 1.76		$ 1.86		$ 1.12		$ 1.27		$ 1.70		$ 1.61		$ 5.51	[8]	$ 5.71	[8]	$ 5.70	[8]
Stock options [Member]
Effect of dilutive securities:
Dilutive securities																	1		1		2
Restricted Stock Units (RSUs) [Member]
Effect of dilutive securities:
Dilutive securities																	3		3		3

[1] Financial results for the third quarter of 2014 include an income tax charge of $122 million relating to a litigation with the Canadian Revenue Agency.

[2] Financial results for the second, third and fourth quarters of 2014 includes pre-tax charges in our Distribution Solutions segment related to our LIFO method of accounting for inventories of $44 million, $142 million and $125 million, which were recorded in cost of sales. Fourth quarter 2014 also includes a $50 million pre-tax charge to cost of sales within our Distribution Solutions segment representing the reversal of a step-up to fair value of Celesio’s inventory at the date of acquisition. Our after-tax portion of this charge (after allocation to noncontrolling interests), was $28 million

[3] Financial results for the first quarter of 2013 include an $81 million pre-tax gain on business combination, which was recorded as a reduction to operating expenses within our Corporate segment.

[4] Financial results for the fourth quarter of 2013 include a pre-tax impairment charge for an equity investment of $191 million recorded in other income, net within our Distribution Solutions segment. Financial results for the fourth quarter of 2013 also include $46 million of pre-tax impairment charges recorded in our Technology Solutions segment of which $36 million was recorded in operating expenses and $10 million was recorded in cost of sales.

[5] Financial results for the third quarter of 2013 include a $40 million pre-tax charge for a legal dispute in our Canadian business which was recorded in operating expenses within our Distribution Solutions segment.

[6] Primarily represents the noncontrolling shareholders’ portion of net loss from Celesio.

[7] Financial results for the third quarter of 2014, include an $80 million of after-tax impairment charge related to our International Technology Business.

[8] Certain computations may reflect rounding adjustments.