Debt (Medium-Term Notes) (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Jul. 15, 2012
Long-term Debt, Weighted Average Interest Rate	3.94%
Medium-term Notes	$ 1,703,900,000	$ 1,632,300,000
Debt Mark To Market Adjustment	31,700,000	35,800,000
Losses related to extinguishments of debt	10,900,000	4,800,000	218,600,000
Repayments of Other Debt	1,203,400,000	151,000,000	710,800,000
Payments for Repurchase of Common Stock	91,500,000	46,100,000	500,100,000
Deferred Gain (Loss) on Discontinuation of Interest Rate Fair Value Hedge	0	15,800,000
Proceeds from Issuance of Long-term Debt	841,900,000	3,300,000	547,300,000
Junior Subordinated Debenture Owed to Unconsolidated Subsidiary Trust	0	436,700,000		436,700,000
6.75% Senior Notes Due March 2012 [Member]
Medium-term Notes	0	250,000,000
Debt Instrument, Face Amount		250,000,000
Senior notes rate		6.75%
Debt Instrument, Maturity Date	Mar. 15, 2012
6.11% Notes Due 2028 [Member]
Debt Instrument, Face Amount	8,500,000
Senior notes rate	6.11%
Debt Instrument, Maturity Date	Jul. 17, 2028
5.50% Senior Notes due 2013 [Member]
Medium-term Notes	0	500,000,000
Debt Instrument, Face Amount	500,000,000
Senior notes rate	5.50%
Losses related to extinguishments of debt	4,100,000
Repayments of Other Debt	512,900,000
Accrued Interest Paid With Debt Retirement	5,800,000
Redemption Premium	7,100,000
Debt Instrument, Maturity Date	Apr. 15, 2013
Deferred Gain (Loss) on Discontinuation of Interest Rate Fair Value Hedge		3,000,000
2.00% Senior Notes Due 2015 [Member]
Medium-term Notes	250,000,000	0
2.05% Senior Notes Due 2017 [Member]
Medium-term Notes	350,000,000	0
Debt Instrument, Face Amount	350,000,000
Senior notes rate	2.05%
Debt Instrument, Maturity Date	Dec. 01, 2017
Debt Instrument, Principal Amount, Change In Control Redemption Percent	101.00%
Debt Instrument, Principal Amount, Redemption Percent	100.00%
Proceeds from Issuance of Long-term Debt	346,800,000
6.25% senior notes due 2018 [Member]
Medium-term Notes	250,000,000	250,000,000
10.60% senior notes due 2019 [Member]
Medium-term Notes	20,700,000	20,700,000
Debt Instrument, Face Amount	300,000,000
Senior notes rate	10.60%
Medium Term Notes, Redemption, Cash Paid Per $1000 Principal Amount			1,437.50
Medium Term Notes, Redemption, Min Principal Amount Subject To Redemption			1,000
Losses related to extinguishments of debt			131,400,000
Repayments of Other Debt			402,200,000
Debt Instrument, Maturity Date	Apr. 15, 2019
Medium Term Notes, Redemption, Principal Amount			279,300,000
4.70% senior notes due 2020 [Member]
Medium-term Notes	550,000,000	550,000,000
Debt Instrument, Face Amount	550,000,000
Senior notes rate	4.70%
Debt Instrument, Maturity Date	Aug. 15, 2020
Debt Instrument, Principal Amount, Change In Control Redemption Percent	101.00%
Debt Instrument, Principal Amount, Redemption Percent	100.00%
Proceeds from Issuance of Long-term Debt			544,900,000
4.00% Senior Notes Due 2022 [Member]
Medium-term Notes	250,000,000	0
6.11% senior notes due 2028 [Member]
Medium-term Notes	1,500,000	10,000,000
2% Notes Due 2015 And 4% Notes Due 2022 [Member]
Debt Instrument, Face Amount	500,000,000
Debt Instrument, Principal Amount, Change In Control Redemption Percent	101.00%
Proceeds from Issuance of Long-term Debt	495,100,000
2% Notes Due June 2015 [Member]
Debt Instrument, Face Amount	250,000,000
Senior notes rate	2.00%
Debt Instrument, Maturity Date	Jun. 13, 2015
4% Notes Due June 2022 [Member]
Debt Instrument, Face Amount	250,000,000
Senior notes rate	4.00%
Debt Instrument, Maturity Date	Jun. 13, 2022
Debt Instrument, Principal Amount, Redemption Percent	100.00%
Accelerated Stock Buyback Program [Member]
Payments for Repurchase of Common Stock			500,000,000
Convertible Preferred Stock [Member]
Liquidation Preference On Preferred Stock	$ 421,200,000