3. Fair Value Measurements Short-term Investments (Details) - Fair Value, Measurements, Recurring [Member] - USD ($) $ in Millions		Dec. 31, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		$ 435.7	$ 382.1
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax		681.7	577.1
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax		(1.8)	(1.6)
Estimated Fair Value	[1]	1,115.6	957.6
Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value	[1]	179.4	156.9
Interest-bearing Deposits [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value		3.6
Municipal Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value	[1]	15.4	6.4
Asset-backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value	[1]	62.5	54.8
Marketable Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value	[1]	767.8	660.1
US Government Sponsored Agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value	[1]	82.5	74.8
Foreign Government Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value	[1]	4.4	4.6
Short-term Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Estimated Fair Value		383.2	328.7
Short-term Investments [Member] | Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		179.7	157.2
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax		0.2	0.1
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax		(0.5)	(0.4)
Estimated Fair Value		179.4	156.9
Short-term Investments [Member] | Interest-bearing Deposits [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		3.6
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax		0.0
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax		0.0
Estimated Fair Value		3.6
Short-term Investments [Member] | Municipal Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		15.5	6.4
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax		0.0	0.0
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax		(0.1)	0.0
Estimated Fair Value		15.4	6.4
Short-term Investments [Member] | Asset-backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		62.2	54.8
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax		0.1	0.0
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax		(0.1)	(0.2)
Estimated Fair Value		62.2	54.6
Short-term Investments [Member] | Marketable Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		32.4	29.4
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax		3.7	2.7
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax		(0.4)	(0.7)
Estimated Fair Value		35.7	31.4
Short-term Investments [Member] | Available-for-sale Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		380.9	327.3
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax		4.1	2.9
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax		(1.8)	(1.5)
Estimated Fair Value		383.2	328.7
Short-term Investments [Member] | US Government Sponsored Agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		83.1	74.9
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax		0.1	0.1
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax		(0.7)	(0.2)
Estimated Fair Value		82.5	74.8
Short-term Investments [Member] | Foreign Government Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		4.4	4.6
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax		0.0	0.0
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax		0.0	0.0
Estimated Fair Value		4.4	4.6
Other Long-term Investments [Member] | Asset-backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		0.3	0.3
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax		0.0	0.0
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax		0.0	(0.1)
Estimated Fair Value		0.3	0.2
Other Long-term Investments [Member] | Marketable Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		54.5	54.5
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax		677.6	574.2
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax		0.0	0.0
Estimated Fair Value		732.1	628.7
Other Long-term Investments [Member] | Available-for-sale Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		54.8	54.8
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax		677.6	574.2
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax		0.0	(0.1)
Estimated Fair Value		$ 732.4	$ 628.9

[1] Available-for-sale investments are included in the following accounts in the Consolidated Balance Sheets (in millions):   December 31,
2016   December 31, 2015         Short-term investments $ 383.2
  $ 328.7
Other investments 732.4
  628.9
Total $ 1,115.6
  $ 957.6