|
Shareholders' Equity (Details) (USD $)
|
0 Months Ended | 3 Months Ended | 6 Months Ended | 1 Months Ended | 0 Months Ended | 3 Months Ended | 1 Months Ended | 6 Months Ended | 1 Months Ended | 6 Months Ended | ||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
|
Jun. 30, 2012
|
Feb. 22, 2012
|
Jun. 30, 2012
|
Jun. 30, 2011
|
Jun. 30, 2012
|
Jun. 30, 2011
|
Jul. 30, 2012
Repurchase of Equity [Member]
|
Jun. 15, 2012
Common Stock [Member]
|
Mar. 15, 2012
Common Stock [Member]
|
Jun. 30, 2012
Common Stock [Member]
|
Dec. 31, 2006
Series D Preferred Stock [Member]
|
Jun. 30, 2012
Series D Preferred Stock [Member]
|
Nov. 30, 2011
Series D Preferred Stock [Member]
|
Mar. 31, 2004
Series C Preferred Stock [Member]
|
Jun. 30, 2012
Series C Preferred Stock [Member]
|
Mar. 23, 2009
Series C Preferred Stock [Member]
|
|
| Class of Stock [Line Items] | ||||||||||||||||
| Dividends declared, Per common share | $ 0.27 | $ 0.26 | $ 0.54 | $ 0.52 | $ 0.27 | $ 0.27 | ||||||||||
| Dividends paid, Per common share | $ 0.27 | $ 0.27 | ||||||||||||||
| Common shares repurchased during the period, Number of shares | 1,200,000 | 71,000 | ||||||||||||||
| Common shares repurchased during period, Aggregate value | $ 91,600,000 | $ 5,300,000 | ||||||||||||||
| Common shares repurchased during period, Average cost per share | $ 74.57 | $ 74.21 | ||||||||||||||
| Share repurchase program, Authorized aggregate amount | 500,000,000 | |||||||||||||||
| Share repurchase program, Remaining authorized aggregate amount | 412,000,000 | |||||||||||||||
| Proceeds from issuance of preference shares | 300,000,000 | 250,000,000 | ||||||||||||||
| Preference shares issued, Shares | 12,000,000 | 10,000,000 | ||||||||||||||
| Preference shares issued, Issuance price per share | $ 25 | $ 25 | ||||||||||||||
| Preference shares, Dividend rate | 6.60% | 6.08% | ||||||||||||||
| Preference shares, Redemption price per share | $ 25 | $ 25 | ||||||||||||||
| Dividends declared and paid, Preference shares | $ 8,750,000 | $ 8,750,000 | $ 17,500,000 | $ 17,500,000 | ||||||||||||