Shareholders' Equity - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions		3 Months Ended		12 Months Ended
	Apr. 17, 2017	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Equity [Line Items]
Dividends declared per common share		$ 0.65	$ 0.65
Shares remitted by employees to satisfy minimum statutory employee tax withholding		12,136
Remitted Shares, Total		$ 3
Cancellation of RSUs to satisfy minimum statutory employee tax withholding		5,700,000
Cancelled RSUs, Total		$ 1,320
Cancellation of stock options to satisfy minimum statutory employee tax withholding and the exercise price of stock options		2,600,000
Cancelled stock options, Total		$ 632
APEX exchanged, par amount			$ 672	$ 1,320
APEX exchanged, fair value			505	$ 1,040
Series E Preferred Stock cancelled, number of shares				9,833
Series F Preferred Stock cancelled, number of shares				3,385
Series E and Series F Preferred Stock cancelled, redemption value			672	$ 1,320
Series E and Series F Preferred Stock cancelled, net carrying value			666	1,310
Difference between fair value of APEX and net carrying value of preferred stock at time of cancellation			$ 161	$ 266
Subsequent Event [Member]
Equity [Line Items]
Dividends declared per common share	$ 0.75
Dividends payable date declared	Apr. 17, 2017
Dividends payable date to be paid	Jun. 29, 2017
Dividends payable date of record	Jun. 01, 2017