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Common and Preferred Stock (Schedule of Share Repurchases) (Detail) - USD ($) $ / shares in Units, $ in Millions | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Schedule of Share Repurchases [Abstract] |  |  |
Number of shares repurchased | 43,000,000 | 16,600,000 | 39,900,000
Average price paid per share | $ 7.55 | $ 6.37 | $ 7.6
Remaining authorization as of December 31 | $ 250 | $ 88 | $ 94

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- Definition Total cost of shares repurchased divided by the total number of shares repurchased. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 30 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6405813&loc=d3e23239-112655 + Details
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