Common and Preferred Stock (Schedule of Share Repurchases) (Detail) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Schedule of Share Repurchases [Abstract]
Number of shares purchased or repurchased	26,400,000	11,100,000	5,800,000
Average price paid per share	$ 7.50	$ 9.12	$ 8.21
Remaining authorization as of December 31	$ 0	$ 101	$ 202

Number of shares that have been repurchased during the period and are being held in treasury.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
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-Name Accounting Standards Codification
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Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
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-Name Accounting Standards Codification
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Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration