Debt (Narrative) (Details) $ / shares in Units, shares in Millions	12 Months Ended
	Dec. 31, 2015 USD ($) $ / shares shares	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)	Sep. 10, 2015 USD ($)	Sep. 15, 2014 USD ($)	Sep. 11, 2014 USD ($)	Aug. 12, 2014 USD ($)	Oct. 09, 2012 USD ($)	Oct. 02, 2012 $ / shares
Debt Instrument [Line Items]
(Gain) loss on extinguishment of debt	$ (9,300,000)	$ 81,100,000	$ 145,300,000
Long-term debt face amount	513,400,000
Line of credit facility, maximum borrowing capacity	$ 3,500,000,000
Line of Credit Maturity Date	Aug. 25, 2020
Long-term debt	$ 15,324,500,000	14,643,900,000
Interest paid	604,000,000	575,900,000	597,200,000
Future maturities of debt in 2016	682,200,000
Future maturities of debt in 2017	927,500,000
Future maturities of debt in 2018	1,267,800,000
Future maturities of debt in 2019	1,282,800,000
Future maturities of debt in 2020	702,900,000
Future maturities of debt Thereafter	$ 10,461,300,000
Convertible Debt [Abstract]
Debt Instrument, Convertible, Conversion Ratio, Shares	13.4886
Debt Instrument, Convertible, Conversion Price | $ / shares	$ 74.1360
Repayments of Long-term Debt	$ 2,697,200,000	1,730,100,000	$ 1,801,900,000
Bridge Loan [Member]
Debt Instrument [Line Items]
Loan Processing Fee	106,600,000
Interest expense	36,800,000
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	61,000,000
(Gain) loss on extinguishment of debt	3,400,000	11,200,000
Convertible Debt [Abstract]
Repurchased Face Amount	$ 13,000,000	52,000,000
Equity Unit Purchase Agreements [Member]
Debt Instrument [Line Items]
Equity Units Issued | shares	25.0
Long-term debt face amount	$ 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 $207.805 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 $207.805 per share but greater than $143.865 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 $143.865 per share, the settlement rate will be 0.3475 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	$ 102,300,000
Equity units contract adjustment payment rate	3.35%
Remarketable Subordinated Notes [Member]
Debt Instrument [Line Items]
Equity Units Ownership Interest Percentage In Remarketable Subordinated Notes	5.00%
Long-term Debt, Percentage Bearing Fixed Interest, Percentage Rate	1.90%
Commercial Paper [Member]
Debt Instrument [Line Items]
Commercial paper authorized	$ 2,500,000,000.0
Commercial paper	$ 682,200,000	$ 0
Weighted average interest rate on commercial paper borrowings	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	$ 330,700,000	$ 956,400,000
Interest expense	$ 32,500,000
Remaining amortization period debt discount	27 years
Effective interest rate for unamortized debt discount	5.13%
Interest expense resulting from the stated interest rate	$ 26,600,000
Interest expense resulting from amortization of the debt discount	$ 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	$ 139.44								$ 60.46
If-converted value per dollar above the conversion price	$ 452,300,000
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%	1.25%
Long-term debt	$ 0	$ 624,300,000
Senior Unsecured Notes [Member] | 2.375%, due 2017 [Member]
Debt Instrument [Line Items]
Long-term Debt, Percentage Bearing Fixed Interest, Percentage Rate	2.375%	2.375%
Long-term debt	$ 399,900,000	$ 398,900,000
Senior Unsecured Notes [Member] | 5.875%, due 2017 [Member]
Debt Instrument [Line Items]
Long-term Debt, Percentage Bearing Fixed Interest, Percentage Rate	5.875%	5.875%
Long-term debt	$ 527,600,000	$ 526,700,000
Senior Unsecured Notes [Member] | 1.875%, due 2018 [Member]
Debt Instrument [Line Items]
Long-term Debt, Percentage Bearing Fixed Interest, Percentage Rate	1.875%	1.875%
Long-term debt	$ 621,900,000	$ 616,400,000
Senior Unsecured Notes [Member] | 2.250%, due 2019 [Member]
Debt Instrument [Line Items]
Debt instrument interest rate							2.25%
Long-term debt face amount							$ 850,000,000
Long-term Debt, Percentage Bearing Fixed Interest, Percentage Rate	2.25%	2.25%
Long-term debt	$ 843,900,000	$ 842,100,000
Senior Unsecured Notes [Member] | 7.000%, due 2019 [Member]
Debt Instrument [Line Items]
Long-term Debt, Percentage Bearing Fixed Interest, Percentage Rate	7.00%	7.00%
Long-term debt	$ 438,900,000	$ 438,500,000
Senior Unsecured Notes [Member] | 4.350%, due 2020 [Member]
Debt Instrument [Line Items]
Long-term Debt, Percentage Bearing Fixed Interest, Percentage Rate	4.35%	4.35%
Long-term debt	$ 702,900,000	$ 695,300,000
Senior Unsecured Notes [Member] | 3.700%, due 2021 [Member]
Debt Instrument [Line Items]
Long-term Debt, Percentage Bearing Fixed Interest, Percentage Rate	3.70%	3.70%
Long-term debt	$ 696,200,000	$ 695,600,000
Senior Unsecured Notes [Member] | 3.125%, due 2022 [Member]
Debt Instrument [Line Items]
Long-term Debt, Percentage Bearing Fixed Interest, Percentage Rate	3.125%	3.125%
Long-term debt	$ 842,700,000	$ 841,600,000
Senior Unsecured Notes [Member] | 3.300%, due 2023 [Member]
Debt Instrument [Line Items]
Long-term Debt, Percentage Bearing Fixed Interest, Percentage Rate	3.30%	3.30%
Long-term debt	$ 992,200,000	$ 991,200,000
Senior Unsecured Notes [Member] | 3.500%, due 2024 [Member]
Debt Instrument [Line Items]
Debt instrument interest rate							3.50%
Long-term debt face amount							$ 800,000,000
Long-term Debt, Percentage Bearing Fixed Interest, Percentage Rate	3.50%	3.50%
Long-term debt	$ 790,900,000	$ 789,800,000
Senior Unsecured Notes [Member] | 5.950%, due 2034 [Member]
Debt Instrument [Line Items]
Long-term Debt, Percentage Bearing Fixed Interest, Percentage Rate	5.95%	5.95%
Long-term debt	$ 444,500,000	$ 444,400,000
Senior Unsecured Notes [Member] | 5.850%, due 2036 [Member]
Debt Instrument [Line Items]
Long-term Debt, Percentage Bearing Fixed Interest, Percentage Rate	5.85%	5.85%
Long-term debt	$ 768,000,000	$ 767,700,000
Senior Unsecured Notes [Member] | 6.375%, due 2037 [Member]
Debt Instrument [Line Items]
Long-term Debt, Percentage Bearing Fixed Interest, Percentage Rate	6.375%	6.375%
Long-term debt	$ 639,600,000	$ 639,300,000
Senior Unsecured Notes [Member] | 5.800%, due 2040 [Member]
Debt Instrument [Line Items]
Long-term Debt, Percentage Bearing Fixed Interest, Percentage Rate	5.80%	5.80%
Long-term debt	$ 193,800,000	$ 206,400,000
Senior Unsecured Notes [Member] | 4.625%, due 2042 [Member]
Debt Instrument [Line Items]
Long-term Debt, Percentage Bearing Fixed Interest, Percentage Rate	4.625%	4.625%
Long-term debt	$ 885,800,000	$ 885,400,000
Senior Unsecured Notes [Member] | 4.650%, due 2043 [Member]
Debt Instrument [Line Items]
Long-term Debt, Percentage Bearing Fixed Interest, Percentage Rate	4.65%	4.65%
Long-term debt	$ 985,500,000	$ 985,000,000
Senior Unsecured Notes [Member] | 4.650%, due 2044 [Member]
Debt Instrument [Line Items]
Debt instrument interest rate							4.65%
Long-term debt face amount							$ 800,000,000
Long-term Debt, Percentage Bearing Fixed Interest, Percentage Rate	4.65%	4.65%
Long-term debt	$ 790,500,000	$ 790,100,000
Senior Unsecured Notes [Member] | 2.300%, due 2018 [Member]
Debt Instrument [Line Items]
Long-term Debt, Percentage Bearing Fixed Interest, Percentage Rate	2.30%	2.30%
Long-term debt	$ 645,900,000	$ 644,300,000
Senior Unsecured Notes [Member] | 5.100%, due 2044 [Member]
Debt Instrument [Line Items]
Long-term Debt, Percentage Bearing Fixed Interest, Percentage Rate	5.10%	5.10%
Long-term debt	$ 593,300,000	$ 593,100,000
Senior Unsecured Notes [Member] | 4.850%, due 2054 [Member]
Debt Instrument [Line Items]
Debt instrument interest rate							4.85%
Long-term debt face amount							$ 250,000,000
Long-term Debt, Percentage Bearing Fixed Interest, Percentage Rate	4.85%	4.85%
Long-term debt	$ 246,600,000	$ 246,500,000
Senior Unsecured Notes [Member] | 5.000%, due 2014 [Member]
Debt Instrument [Line Items]
Debt instrument interest rate					5.00%
Repurchased face amount					$ 500,000,000
Early repayment of senior debt	512,300,000
(Gain) loss on extinguishment of debt	2,300,000
Senior Unsecured Notes [Member] | 5.250%, due 2016 [Member]
Debt Instrument [Line Items]
Debt instrument interest rate						5.25%
Repurchased face amount						$ 1,097,900,000
Early repayment of senior debt	1,178,200,000
(Gain) loss on extinguishment of debt	67,600,000
Federal Home Loan Bank Advances [Member]
Debt Instrument [Line Items]
Short-term FHLB borrowings outstanding	$ 540,000,000	$ 400,000,000
Debt instrument interest rate	0.424%	0.195%
TerminatedRevolvingCreditFacility [Domain]
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity	$ 2,000,000,000
Line of Credit Maturity Date	Sep. 29, 2016