Fair Value Measurements (Details) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2014		Dec. 31, 2013
Available-for-sale securities:
Available-for-sale securities	$ 2,944.2		$ 2,882.2
Trading securities:
Trading securities	16.4	[1]	15.4	[1]
Fair Value Measurements (Textuals)
Restricted investments	61.3		83.6
Purchases of Privately-Held Investments	4.2
Estimate of Fair Value Measurement [Member] | Fair Value, Measurements, Recurring [Member]
Derivative assets:
Total assets measured at fair value	3,044.7		2,928.7
Liabilities measured at fair value:
Other accrued liabilities	(0.2)		(0.7)
Total liabilities measured at fair value	(0.2)		(0.7)
Cash equivalents	1,094.6		996.2
Restricted investments	65.4		87.6
Short-term investments	460.5		561.9
Long-term investments	1,340.1		1,251.9
Prepaid expenses and other current assets measured at fair value	41.8		3.0
Other long-term assets	42.3		28.1
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Derivative assets:
Total assets measured at fair value	1,553.5		1,374.9
Liabilities measured at fair value:
Other accrued liabilities	0		0
Total liabilities measured at fair value	0		0
Cash equivalents	1,073.9		965.1
Restricted investments	65.4		87.6
Short-term investments	212.5		246.5
Long-term investments	201.7		75.7
Prepaid expenses and other current assets measured at fair value	0		0
Other long-term assets	0		0
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Derivative assets:
Total assets measured at fair value	1,448.9		1,525.7
Liabilities measured at fair value:
Other accrued liabilities	(0.2)		(0.7)
Total liabilities measured at fair value	(0.2)		(0.7)
Cash equivalents	20.7		31.1
Restricted investments	0		0
Short-term investments	248.0		315.4
Long-term investments	1,138.4		1,176.2
Prepaid expenses and other current assets measured at fair value	41.8		3.0
Other long-term assets	0		0
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Derivative assets:
Total assets measured at fair value	42.3		28.1
Liabilities measured at fair value:
Other accrued liabilities	0		0
Total liabilities measured at fair value	0		0
Cash equivalents	0		0
Restricted investments	0		0
Short-term investments	0		0
Long-term investments	0		0
Prepaid expenses and other current assets measured at fair value	0		0
Other long-term assets	42.3		28.1
Foreign exchange contract [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Measurements, Recurring [Member]
Derivative assets:
Derivative assets	3.0		3.0
Liabilities measured at fair value:
Derivative liabilities	(0.2)		(0.7)
Foreign exchange contract [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Derivative assets:
Derivative assets	0		0
Liabilities measured at fair value:
Derivative liabilities	0		0
Foreign exchange contract [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Derivative assets:
Derivative assets	3.0		3.0
Liabilities measured at fair value:
Derivative liabilities	(0.2)		(0.7)
Foreign exchange contract [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Derivative assets:
Derivative assets	0		0
Liabilities measured at fair value:
Derivative liabilities	0		0
Warrant [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Measurements, Recurring [Member]
Derivative assets:
Warrant on Palo Alto Network Common Stock	38.8
Warrant [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Derivative assets:
Warrant on Palo Alto Network Common Stock	0
Warrant [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Derivative assets:
Warrant on Palo Alto Network Common Stock	38.8
Warrant [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Derivative assets:
Warrant on Palo Alto Network Common Stock	0
Asset-backed Securities [Member]
Available-for-sale securities:
Available-for-sale securities	259.1		249.9
Asset-backed Securities [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale securities:
Available-for-sale securities	259.1		249.9
Asset-backed Securities [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale securities:
Available-for-sale securities	0		0
Asset-backed Securities [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale securities:
Available-for-sale securities	259.1		249.9
Asset-backed Securities [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale securities:
Available-for-sale securities	0		0
Certificates of deposit [Member]
Available-for-sale securities:
Available-for-sale securities	10.2		27.6
Certificates of deposit [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale securities:
Available-for-sale securities	10.2		27.6
Certificates of deposit [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale securities:
Available-for-sale securities	0		0
Certificates of deposit [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale securities:
Available-for-sale securities	10.2		27.6
Certificates of deposit [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale securities:
Available-for-sale securities	0		0
Commercial paper [Member]
Available-for-sale securities:
Available-for-sale securities	15.8		6.9
Commercial paper [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale securities:
Available-for-sale securities	15.8		6.9
Commercial paper [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale securities:
Available-for-sale securities	0		0
Commercial paper [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale securities:
Available-for-sale securities	15.8		6.9
Commercial paper [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale securities:
Available-for-sale securities	0		0
Corporate debt securities [Member]
Available-for-sale securities:
Available-for-sale securities	816.7		815.3
Corporate debt securities [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale securities:
Available-for-sale securities	816.7		815.3
Corporate debt securities [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale securities:
Available-for-sale securities	0		0
Corporate debt securities [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale securities:
Available-for-sale securities	816.7		815.3
Corporate debt securities [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale securities:
Available-for-sale securities	0		0
Foreign government debt securities [Member]
Available-for-sale securities:
Available-for-sale securities	28.5		10.7
Foreign government debt securities [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale securities:
Available-for-sale securities	28.5		10.7
Foreign government debt securities [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale securities:
Available-for-sale securities	0		0
Foreign government debt securities [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale securities:
Available-for-sale securities	28.5		10.7
Foreign government debt securities [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale securities:
Available-for-sale securities	0		0
Government-sponsored enterprise obligations [Member]
Available-for-sale securities:
Available-for-sale securities	226.1		306.2
Government-sponsored enterprise obligations [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale securities:
Available-for-sale securities	226.1		306.2
Government-sponsored enterprise obligations [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale securities:
Available-for-sale securities	0		0
Government-sponsored enterprise obligations [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale securities:
Available-for-sale securities	226.1		306.2
Government-sponsored enterprise obligations [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale securities:
Available-for-sale securities	0		0
Money market funds [Member]
Available-for-sale securities:
Available-for-sale securities	1,135.1		1,043.7
Money market funds [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale securities:
Available-for-sale securities	1,135.1	[2]	1,043.7	[3]
Money market funds [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale securities:
Available-for-sale securities	1,135.1	[2]	1,043.7	[3]
Money market funds [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale securities:
Available-for-sale securities	0	[2]	0	[3]
Money market funds [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale securities:
Available-for-sale securities	0	[2]	0	[3]
Mutual funds [Member]
Available-for-sale securities:
Available-for-sale securities	4.1		4.0
Mutual funds [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale securities:
Available-for-sale securities	4.1	[4]	4.0	[4]
Trading securities:
Trading securities	16.4	[5]	15.4	[5]
Mutual funds [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale securities:
Available-for-sale securities	4.1	[4]	4.0	[4]
Trading securities:
Trading securities	16.4	[5]	15.4	[5]
Mutual funds [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale securities:
Available-for-sale securities	0	[4]	0	[4]
Trading securities:
Trading securities	0	[5]	0	[5]
Mutual funds [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale securities:
Available-for-sale securities	0	[4]	0	[4]
Trading securities:
Trading securities	0	[5]	0	[5]
Publicly-traded equity securities [Member]
Available-for-sale securities:
Available-for-sale securities	93.0		114.6
Publicly-traded equity securities [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale securities:
Available-for-sale securities	93.0		114.6
Publicly-traded equity securities [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale securities:
Available-for-sale securities	93.0		114.6
Publicly-traded equity securities [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale securities:
Available-for-sale securities	0		0
Publicly-traded equity securities [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale securities:
Available-for-sale securities	0		0
US government securities [Member]
Available-for-sale securities:
Available-for-sale securities	355.6		303.3
US government securities [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale securities:
Available-for-sale securities	355.6		303.3
US government securities [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale securities:
Available-for-sale securities	304.9		197.2
US government securities [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale securities:
Available-for-sale securities	50.7		106.1
US government securities [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale securities:
Available-for-sale securities	0		0
Available-for-sale securities [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale securities:
Available-for-sale securities	2,944.2		2,882.2
Available-for-sale securities [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale securities:
Available-for-sale securities	1,537.1		1,359.5
Available-for-sale securities [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale securities:
Available-for-sale securities	1,407.1		1,522.7
Available-for-sale securities [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale securities:
Available-for-sale securities	0		0
Debt Securities [Member]
Available-for-sale securities:
Available-for-sale securities	1,712.0		1,719.9
Debt Securities [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Measurements, Recurring [Member]
Trading securities:
Privately-held securities	42.3		28.1
Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Trading securities:
Privately-held securities	0		0
Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Trading securities:
Privately-held securities	0		0
Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Trading securities:
Privately-held securities	$ 42.3		$ 28.1

[1] Balance includes the Company's non-qualified deferred compensation plan assets.

[2] Balance includes $61.3 million of restricted investments measured at fair market value related to the Company's D&O Trust and acquisitions related escrows.

[3] Balance includes $83.6 million of restricted investments measured at fair market value related to the Company's D&O Trust and acquisitions related escrows.

[4] Balance relates to restricted investments measured at fair market value related to the Company's India Gratuity Trust.

[5] Balance relates to investments measured at fair value related to the Company's non-qualified deferred compensation plan assets.