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Stock Benefit Plans (Narrative) (Details) $ / shares in Units, $ in Millions | 1 Months Ended | 12 Months Ended |
--- | --- | --- | ---
May 31, 2007 shares | Jul. 31, 2002 shares | Dec. 31, 2017 USD ($) purchase $ / shares shares | Dec. 31, 2016 USD ($) $ / shares shares | Dec. 31, 2015 USD ($) $ / shares | May 19, 2011 equity_incentive_plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |
Average volatility periods ending on fifteen anniversaries prior to valuation date |  |  | 15 years |  |  |
Options, weighted-average grant-date fair value (in dollars per share) | $ / shares |  |  | $ 15.01 | $ 11.57 | $ 11.34 |
Total intrinsic value of options exercised | $ |  |  | $ 195.3 | $ 137.7 | $ 124.6 |
Cash received from the exercise of stock options | $ |  |  | $ 126.7 | 105.4 | 134.7 |
Restricted Stock | Certain grants in 2005 |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |
Vesting period, years |  |  | 3 years |  |  |
Restricted Stock Units And Performance Stock Units |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |
Vesting period, years |  |  | 3 years |  |  |
Total fair value of deferred stock units | $ |  |  | $ 117.1 | $ 91.4 | $ 114.3 |
Restricted Stock Units (RSUs) |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |
Weighted-average grant-date fair value (in dollars per share) | $ / shares |  |  | $ 73.23 | $ 57.54 | $ 56.81 |
Stock Options |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |
Daily closing price observation period |  |  | 10 years |  |  |
Average volatility periods ending on fifteen anniversaries prior to valuation date |  |  | 10 years |  |  |
Unrecognized compensation cost related to option awards | $ |  |  | $ 14.9 |  |  |
Weighted-average period over which that cost is expected to be recognized, years |  |  | 1 year 3 months 40 days |  |  |
Restricted Stock Units, Restricted Stock and Performance Units |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |
Weighted-average period over which that cost is expected to be recognized, years |  |  | 1 year 28 days |  |  |
Unrecognized compensation cost | $ |  |  | $ 197.4 |  |  |
Performance Shares |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |
Performance-based restricted stock unit payable range minimum |  |  | 0.00% |  |  |
Performance-based restricted stock unit payable range maximum |  |  | 200.00% |  |  |
Performance period |  |  | 3 years |  |  |
Weighted-average grant-date fair value (in dollars per share) | $ / shares |  |  | $ 73.20 | $ 57.47 | $ 57.33 |
Shares distributable in period (in shares) |  |  |  | 254,455 |  |
Performance Shares | PSUs Awarded in 2012 |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |
Target payout percentage |  |  |  | 120.00% |  |
Performance Shares | PSUs Awarded in 2013 |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |
Target payout percentage |  |  |  | 137.00% |  |
Performance Shares | PSUs Awarded in 2014 |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |
Target payout percentage |  |  |  | 167.00% |  |
Award Plans 2000 |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |
Number of previous equity plans replaced | equity_incentive_plan |  |  |  |  |  | 2
Incentive and Stock Award Plan 2011 |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |
Awards authorized (not more than 23.2 million shares for the 2011 Plan and 35.6 million shares for the 1999 Plan) (in shares) |  |  | 23,200,000 |  |  |
Incentive and Stock Award Plan 2011 | Stock Options |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |
Stock options vesting percentage |  |  | 25.00% |  |  |
Contractual term of stock option awards |  |  | 10 years |  |  |
Employee Stock Purchase Plan 1999 | Employee Stock |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |
Awards authorized (not more than 23.2 million shares for the 2011 Plan and 35.6 million shares for the 1999 Plan) (in shares) |  |  | 35,600,000 |  |  |
Number of share purchase times per plan year | purchase |  |  | 4 |  |  |
Stock option price percent |  |  | 95.00% |  |  |
Reduction in the shares available (in shares) |  |  | 10,000,000 |  |  |
Shares purchased by employees (in shares) |  |  | 428,244 |  |  |
Shares available for issuance under the plan (in shares) |  |  | 1,353,166 |  |  |
International Plan | Employee Stock |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |
Awards authorized (not more than 23.2 million shares for the 2011 Plan and 35.6 million shares for the 1999 Plan) (in shares) |  |  | 12,000,000 |  |  |
Shares purchased by employees (in shares) |  |  | 121,292 |  |  |
Shares available for issuance under the plan (in shares) |  |  | 2,491,910 |  |  |
Shares due to shareholder action (in shares) | 4,000,000 | 5,000,000 |  |  |  |

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