Fair Value Of Financial Instruments (Fair Value Of Financial Assets Measured On Recurring Basis) (Details) $ in Millions	Dec. 31, 2016 USD ($)
ASSETS
Total assets measured at fair value	$ 16,032.0
Cash And Cash Equivalents [Member] | Money Market Funds [Member]
ASSETS
Total cash and cash equivalents	1,726.0
Investments [Member] | Corporate Bonds [Member]
ASSETS
Total investments	13,289.0
Investments [Member] | Asset-Backed Securities [Member]
ASSETS
Total investments	1,017.0
Level 1 [Member]
ASSETS
Total assets measured at fair value	1,726.0
Level 1 [Member] | Cash And Cash Equivalents [Member] | Money Market Funds [Member]
ASSETS
Total cash and cash equivalents	1,726.0
Level 2 [Member]
ASSETS
Total assets measured at fair value	14,306.0
Level 2 [Member] | Investments [Member] | Corporate Bonds [Member]
ASSETS
Total investments	13,289.0
Level 2 [Member] | Investments [Member] | Asset-Backed Securities [Member]
ASSETS
Total investments	$ 1,017.0