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Shareholders' Equity (Details Textual) - USD ($) $ / shares in Units, $ in Millions | 3 Months Ended | 6 Months Ended |
--- | --- | --- | ---
Jun. 30, 2015 | Mar. 31, 2015 | Jun. 30, 2014 | Jun. 30, 2015 | Jun. 30, 2014 | Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |
Net of tax unrealized gains (losses) related to credit-only impaired securities | $ 57 | $ 57 |  | $ 57 |  | $ 58
Common Stock options issued under stock incentive plan, average exercise price |  |  |  | $ 63.15 | $ 56.44 |
Compensation expense related to stock incentive plans | $ 7 |  | $ 7 | $ 13 | $ 14 |
Stock Incentive Plan [Member] |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |
Restricted Common Stock, shares issued |  |  |  | 171,130 |  |
Restricted Common Stock, fair value per share |  |  |  | $ 63.15 |  |
Common Stock options issued under stock incentive plan |  |  |  | 716,818 |  |
Common Stock options issued under stock incentive plan, average exercise price |  |  |  | $ 63.15 |  |
Annual Equity Bonus Plan [Member] |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |
Other benefit plans, shares |  | 54,732 |  |  |  |
Common Stock issued, fair value per share |  | $ 62.55 |  |  |  |

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- Definition Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SAB TOPIC 14.F) -URI http://asc.fasb.org/extlink&oid=27013229&loc=d3e301413-122809 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5047-113901 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (h)(1)(i) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Staff Accounting Bulletin (SAB) -Number Topic 14 -Section F + Details
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