Preferred and Common Stock - Schedule of Activity for Stock Options and Stock Awards (Detail) shares in Millions	12 Months Ended
	Dec. 31, 2015 $ / shares shares
Schedule Of Stock Option Activity [Line Items]
Number of options, Exercised	(23.3)
Stock Options [Member]
Schedule Of Stock Option Activity [Line Items]
Number of options, Outstanding beginning of year	32.0
Number of options, Granted	3.0
Number of options, Assumed at acquisition	2.0
Number of options, Exercised	(3.0)
Converted	0.0
Number of options, Expired or forfeited	(1.0)
Number of options, Performance share adjustment	0.0
Number of options, Outstanding end of year	33.0
Weighted average exercise price, Outstanding beginning of year | $ / shares	$ 11.26
Weighted average exercise price, granted | $ / shares	15.55
Weighted average exercise price, Assumed at Acquisition | $ / shares	11.24
Weighted average exercise price, exercised | $ / shares	8.95
Weighted average exercise price, Converted | $ / shares	0
Weighted average exercise price, expired or forfeited | $ / shares	13.39
Weighted average exercise price, Performance share adjustment | $ / shares	0
Weighted average exercise price Outstanding, end of year | $ / shares	$ 11.91
Stock Awards [Member]
Schedule Of Stock Option Activity [Line Items]
Number of awards, Outstanding beginning of year	19.0
Number of awards, Granted	7.0
Number of awards, Assumed at acquisition	1.0
Number of awards, Exercised	0.0
Number of awards, Converted	(5.0)
Number of awards, Expired or forfeited	(1.0)
Number of awards, Performance share adjustment	(1.0)
Number of awards, Outstanding end of year	20.0
Weighted average FMV per award, Outstanding beginning of year | $ / shares	$ 9.98
Weighted average FMV per award, Granted | $ / shares	14.85
Weighted average FMV per award, Assumed at acquisition | $ / shares	9.96
Weighted average FMV per award, Exercised | $ / shares	0
Weighted average FMV per award, Converted | $ / shares	10.08
Weighted average FMV per award, Expired or forfeited | $ / shares	11.64
Weighted average FMV per award, Performance share adjustment | $ / shares	10.96
Weighted average FMV per award, Outstanding, end of year | $ / shares	$ 11.38