Debt (details) - Repayment (USD $) In Millions, unless otherwise specified	0 Months Ended
	Mar. 15, 2013	May 29, 2012	Jun. 15, 2012
5.00% Senior notes due March 15, 2013 [Member]
Debt repayment
Debt, principal amount repaid	$ 500.0
Interest rate (percent)	5.00%
6.25% Fixed-to-floating rate junior subordinated debentures due March 15, 2067 [Member]
Debt repayment
Debt, principal amount repaid		8.5
Interest rate (percent)		6.25%
5.375% Senior notes due June 15, 2012 [Member]
Debt repayment
Debt, principal amount repaid			$ 250.0
Interest rate (percent)			5.375%