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Significant Accounting Policies (Details) | 12 Months Ended |
--- | --- | ---
Mar. 31, 2016 USD ($) customer segment | Mar. 31, 2015 USD ($) | Mar. 31, 2014 USD ($) | Mar. 31, 2013 USD ($)
Accounting Policies [Abstract] |  |  |  |
Number of operating segments | segment | 2 |  |  |
Restricted cash balance | $ 939,000,000 | $ 0 |  |
Significant Accounting Policies [Line Items] |  |  |  |
LIFO inventory, percentage | 74.00% | 73.00% |  |
LIFO reserve | $ 1,012,000,000 | $ 768,000,000 |  |
Charges associated with last-in-first-out inventory method | $ 244,000,000 | 337,000,000 | $ 311,000,000 |
LIFO inventory, excess of market |  |  |  | $ 60,000,000
LIFO to market adjustment |  |  | 60,000,000 |
Capitalized software held for sale, useful life | 3 years |  |  |
Capitalized software held for internal use, net | $ 435,000,000 | 435,000,000 |  |
Capitalized software held for internal use, accumulated amortization | 1,130,000,000 | 1,112,000,000 |  |
Sales returns from customers | 3,100,000,000 | 2,700,000,000 | 1,900,000,000 |
Supplier reserves | 144,000,000 | 167,000,000 |  |
Current net deferred tax liabilities | 0 | (1,820,000,000) |  |
New Accounting Pronouncement, Early Adoption, Effect |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |
Current net deferred tax liabilities | $ 2,000,000,000 |  |  |
Minimum |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |
Property, plant and equipment, useful life | 1 year |  |  |
Intangible assets, useful life | 1 year |  |  |
Capitalized software held for internal use, useful life | 1 year |  |  |
Maximum |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |
Property, plant and equipment, useful life | 30 years |  |  |
Intangible assets, useful life | 38 years |  |  |
Capitalized software held for internal use, useful life | 10 years |  |  |
Selling, Distribution and Administrative Expenses |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |
Shipping and handling costs | $ 789,000,000 | $ 819,000,000 | $ 535,000,000 |
Customer Concentration Risk | Sales Revenue, Net |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |
Number of largest customers | customer | 10 |  |  |
Percentage of total consolidated revenues | 52.40% |  |  |
Customer Concentration Risk | Sales Revenue, Net | CVS |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |
Percentage of total consolidated revenues | 20.30% |  |  |
Customer Concentration Risk | Accounts Receivable |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |
Number of largest customers | customer | 10 |  |  |
Percentage of total consolidated revenues | 32.00% |  |  |
Customer Concentration Risk | Accounts Receivable | CVS |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |
Percentage of total consolidated revenues | 18.00% |  |  |

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