Debt (Narrative) (Details) $ / shares in Units, shares in Millions	12 Months Ended
	Dec. 31, 2016 USD ($) $ / shares shares	Dec. 31, 2015 USD ($) shares	Dec. 31, 2014 USD ($)	Jan. 23, 2017 USD ($)	Sep. 10, 2015 USD ($)	Oct. 09, 2012 USD ($)	Oct. 02, 2012 $ / shares
Debt Instrument [Line Items]
(Gain) loss on extinguishment of debt	$ 0	$ (9,300,000)	$ 81,100,000
Long-term debt face amount	513,400,000
Senior revolving credit facility, maximum borrowing capacity	$ 3,500,000,000
Senior revolving credit facility, maturity date	Aug. 25, 2020
Long-term debt	$ 15,286,900,000	15,324,500,000
Interest paid	594,900,000	604,000,000	575,900,000
Future maturities of debt in 2017	1,557,400,000
Future maturities of debt in 2018	1,271,800,000
Future maturities of debt in 2019	1,285,000,000
Future maturities of debt in 2020	700,000,000
Future maturities of debt in 2021	696,900,000
Future maturities of debt Thereafter	$ 9,775,800,000
Convertible Debt [Abstract]
Debt Instrument, Convertible, Conversion Ratio, Shares	13.6368
Debt Instrument, Convertible, Conversion Price | $ / shares	$ 73.3306
Repayments of Long-term Debt	$ 0	2,697,200,000	$ 1,730,100,000
Bridge Loan [Member]
Debt Instrument [Line Items]
Bridge facility obtainment fees incurred		106,600,000
Interest expense	104,000,000	36,800,000
Bridge Loan	$ 22,500,000,000
Bridge Loan [Member] | Subsequent Event [Member]
Debt Instrument [Line Items]
Bridge Loan				$ 19,500,000,000
Unamortized bridge facility extension fee				$ 97,500,000
Senior Convertible Debentures [Member]
Debt Instrument [Line Items]
(Gain) loss on extinguishment of debt		(12,700,000)
Convertible Debt [Abstract]
Repurchased Face Amount		920,000,000
Aggregate principal amount of convertible debentures surrendered for conversion		66,600,000
Repayments of Long-term Debt		2,055,700,000
Other senior unsecured notes [Member]
Debt Instrument [Line Items]
Early repayment of senior debt		16,200,000
(Gain) loss on extinguishment of debt		3,400,000
Convertible Debt [Abstract]
Repurchased Face Amount		$ 13,000,000
Equity Unit Purchase Agreements [Member]
Debt Instrument [Line Items]
Equity Units Issued | shares	25.0	25.0
Long-term debt face amount	$ 1,250,000,000	$ 1,250,000,000
Equity Unit Stated Value Per Unit		50
Proceeds from Issuance of Subordinated Long-term Debt		1,228,800,000
Forward Contract Indexed to Issuer's Equity, Settlement Alternatives	On May 1, 2018, if the applicable market value of our common stock is equal to or greater than $207.6487 per share, the settlement rate will be 0.2406 shares of our common stock. If the applicable market value of our common stock is less than $207.6487 per share but greater than $143.7568 per share, the settlement rate will be a number of shares of our common stock equal to $50 (whole dollars) divided by the applicable market value of our common stock. If the applicable market value of common stock is less than or equal to $143.7568 per share, the settlement rate will be 0.3479 shares of our common stock. Holders of the Equity Units may elect early settlement at a minimum settlement rate of 0.2406 shares of our common stock for each purchase contract being settled.
Stock purchase contract liability, present value	$ 62,000,000	$ 102,300,000
Equity units contract adjustment payment rate	3.35%	3.35%
Remarketable Subordinated Notes [Member]
Debt Instrument [Line Items]
Equity Units Ownership Interest Percentage In Remarketable Subordinated Notes	5.00%	5.00%
Long-term Debt, Percentage Bearing Fixed Interest, Percentage Rate	1.90%	1.90%
Commercial Paper [Member]
Debt Instrument [Line Items]
Commercial paper authorized	$ 2,500,000,000.0
Commercial paper	$ 629,000,000	$ 682,200,000
Weighted average interest rate on commercial paper borrowings	0.9715%	0.705%
Senior Convertible Debentures [Member] | 2.750%, due 2042 [Member]
Debt Instrument [Line Items]
Debt instrument interest rate	2.75%
Long-term debt face amount						$ 1,500,000,000
Long-term Debt, Percentage Bearing Fixed Interest, Percentage Rate	2.75%	2.75%				2.75%
Maturity date on long-term debt	Oct. 15, 2042
Long-term debt	$ 334,100,000	$ 330,700,000
Interest expense	$ 17,300,000	32,500,000
Remaining amortization period debt discount	26 years
Effective interest rate for unamortized debt discount	5.13%
Interest expense resulting from the stated interest rate	$ 14,100,000	26,600,000
Interest expense resulting from amortization of the debt discount	$ 3,200,000	5,900,000
Convertible Debt [Abstract]
Number of trading days in 30 day period greater than 130%	20 days
Number of trading days exceeding 130%	30 days
Product of Conversion to Stock Price	130.00%
Required days trading price less than 98%	5 days
Measurement Period for testing	10 days
Percent of Conversion Price to Closing Price	98.00%
Earliest Date for Conversion	Apr. 15, 2042
Date debentures redeemable at our option	Oct. 20, 2022
Conversion premium (%)							25.00%
Closing Price Company Stock | $ / shares	$ 143.77						$ 60.46
If-converted value per dollar above the conversion price	$ 493,200,000
Debt Instrument, Convertible, Conversion Ratio, Shares	13.2319
Debt Instrument, Convertible, Conversion Price | $ / shares							$ 75.575
Senior Unsecured Notes [Member] | 1.250%, due 2015 [Member]
Debt Instrument [Line Items]
Repurchased face amount					$ 625,000,000
Long-term Debt, Percentage Bearing Fixed Interest, Percentage Rate					1.25%
Federal Home Loan Bank Advances [Member]
Debt Instrument [Line Items]
Short-term FHLB borrowings outstanding	$ 440,000,000	$ 540,000,000
Debt instrument interest rate	0.643%	0.424%