Stock-Based Compensation (Narrative) (Details) - USD ($)
$ / shares in Units, shares in Millions, $ in Millions |
3 Months Ended |
6 Months Ended |
29 Months Ended |
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Sep. 30, 2016 |
Sep. 30, 2015 |
Sep. 30, 2016 |
Sep. 30, 2015 |
Sep. 30, 2016 |
May 04, 2015 |
May 05, 2014 |
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
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| Excess Tax Benefit from Share-based Compensation, Financing Activities |
$ 4
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$ 25
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$ 37
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$ 65
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| Minimum |
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| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
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| Percentage range of shares received at vesting based on total stockholder return ("TSR") |
0.00%
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0.00%
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0.00%
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| Maximum |
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| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
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| Percentage range of shares received at vesting based on total stockholder return ("TSR") |
200.00%
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200.00%
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200.00%
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| Market-Based Restricted Stock Units [Member] |
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| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
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| Unrecognized compensation cost related to stock options and restricted stock rights |
$ 49
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$ 49
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$ 49
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| Weighted-average grant date fair values of restricted stock rights granted |
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$ 98.04
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| Maximum number of common shares to be earned during the performance period, Grants |
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0.7
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| Maximum number of common shares to be earned during the performance period, outstanding |
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1.3
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| Market-Based Restricted Stock Units [Member] | Target |
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| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
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| Percentage of target of presented shares granted that may potentially vest |
100.00%
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100.00%
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100.00%
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| Employee Stock Option [Member] |
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| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
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| Unrecognized compensation cost related to stock options and restricted stock rights |
$ 5
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$ 5
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$ 5
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| Weighted-average service period |
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1 year
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| Restricted Stock Rights [Member] |
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| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
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| Unrecognized compensation cost related to stock options and restricted stock rights |
$ 352
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$ 352
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$ 352
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| Weighted-average service period |
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1 year 9 months
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| Weighted-average grant date fair values of restricted stock rights granted |
$ 79.16
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$ 75.31
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| May 2014 Repurchase Program [Member] [Member] |
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| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
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| Amount of common stock authorized for repurchase |
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$ 750
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| Stock Repurchased and Retired During Period, Shares |
0.0
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0.0
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0.0
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1.0
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9.2
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| Repurchase and retirement of common stock |
$ 0
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$ 0
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$ 0
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$ 57
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$ 394
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| May 2015 Repurchase Program [Member] [Member] |
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| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
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| Amount of common stock authorized for repurchase |
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$ 1,000
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| Stock Repurchased and Retired During Period, Shares |
1.6
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1.8
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3.5
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3.0
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| Repurchase and retirement of common stock |
$ 127
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$ 126
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$ 256
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$ 201
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| Repurchase Program, Total [Member] |
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| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
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| Stock Repurchased and Retired During Period, Shares |
1.6
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1.8
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3.5
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4.0
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| Repurchase and retirement of common stock |
$ 127
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$ 126
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$ 256
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$ 258
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| Stock-based compensation expense [Member] |
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| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
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| Deferred Income Tax Expense (Benefit) |
$ 9
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$ 18
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