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Subsequent Events - Additional Information (Detail) - USD ($) $ / shares in Units, shares in Millions |  |  |  | 3 Months Ended |  |  |
--- | --- | --- | --- | --- | --- | --- | ---
Apr. 26, 2017 | Apr. 24, 2017 | Feb. 14, 2017 | Jun. 30, 2017 | Mar. 31, 2017 | Mar. 31, 2016 | Apr. 25, 2017 | Apr. 19, 2017 | Apr. 05, 2017
Subsequent Event [Line Items] |  |  |  |  |  |  |  |  |
Pre-tax gain on sale of common stock |  |  | $ 351,000,000 |  |  |  |  |  |
Interest expense |  |  |  |  | $ 115,000,000 | $ 121,000,000 |  |  |
Scenario, Forecast [Member] |  |  |  |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |  |  |  |
Pre-tax gain on sale of common stock |  |  |  | $ 167,000,000 |  |  |  |  |
Minimum [Member] | Scenario, Forecast [Member] |  |  |  |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |  |  |  |
Interest expense |  |  |  | 50,000,000 |  |  |  |  |
Maximum [Member] | Scenario, Forecast [Member] |  |  |  |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |  |  |  |
Interest expense |  |  |  | $ 60,000,000 |  |  |  |  |
Subsequent Event [Member] |  |  |  |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |  |  |  |
Aggregate principal amount |  |  |  |  |  |  |  | $ 795,000,000 |
Amount of notes purchased |  | $ 295,000,000 |  |  |  |  |  |  |
Senior notes purchased for cash | $ 77,000,000 | $ 320,000,000 |  |  |  |  |  |  |
Remaining amount of notes agreed to sell by purchaser |  |  |  |  |  |  | $ 500,000,000 |  |
Senior notes purchased for shares | 12,958,767 |  |  |  |  |  |  |  |
Tender offers expiration date | May 02, 2017 |  |  |  |  |  |  |  |
Debt instrument conversion price | $ 35.91 |  |  |  |  |  |  |  |
Subsequent Event [Member] | 2018 Notes [Member] |  |  |  |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |  |  |  |
Maximum purchase of aggregate principal amount |  |  |  |  |  |  |  |  | $ 1,000,000,000

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- Definition This item represents the gain (loss) realized during the period from the sale of investments accounted for under the cost method of accounting and any losses recognized thereon for impairments of other than a temporary nature. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 225 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-04(3)) -URI http://asc.fasb.org/extlink&oid=6879464&loc=d3e573970-122913 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 225 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03(7)(c)) -URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 225 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-04(13)(h)) -URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 225 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03(9)(a)) -URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688 + Details
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