Shareholders' Equity - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions		3 Months Ended		9 Months Ended
	Oct. 17, 2016	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Equity [Line Items]
Dividends declared per common share		$ 0.65	$ 0.65	$ 1.95	$ 1.90
Shares remitted by employees to satisfy minimum statutory employee tax withholding				49,374
Remitted Shares, Total				$ 7
Cancellation of RSUs to satisfy minimum statutory employee tax withholding				6,100,000
Cancelled RSUs, Total				$ 920
Cancellation of stock options to satisfy minimum statutory employee tax withholding				660,271
Cancelled stock options, Total				$ 106
APEX exchanged, par amount		$ 650		1,320
APEX exchanged, fair value				$ 1,040
Series E Preferred Stock cancelled, number of shares		4,861		9,833
Series F Preferred Stock cancelled, number of shares		1,639		3,385
Series E and Series F Preferred Stock cancelled, redemption value		$ 650		$ 1,320
Series E and Series F Preferred Stock cancelled, net carrying value				1,310
Difference between fair value of APEX and net carrying value of preferred stock at time of cancellation		$ 105		$ 266
Subsequent Event [Member]
Equity [Line Items]
Dividends declared per common share	$ 0.65
Dividends payable date declared	Oct. 17, 2016
Dividends payable date to be paid	Dec. 29, 2016
Dividends payable date of record	Dec. 01, 2016