Reconciliation of Net Income to Net Income Available to Common Shareholders (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions		3 Months Ended
		Mar. 31, 2017	Mar. 31, 2016
Document Period End Date		Mar. 31, 2017
Net Income (Loss) Attributable to Parent		$ 468	$ 447
Dividends, Preferred Stock, Cash	[1]	(17)	(17)
Undistributed Earnings (Loss) Allocated to Participating Securities, Basic		0	0
Net Income (Loss) Available to Common Stockholders, Basic		$ 451	$ 430
Average basic common shares		490,091	505,482
Stock options		1,000	2,000
Restricted stock		5,000	3,000
Weighted Average Number of Shares Outstanding, Diluted		496,002	509,931
Net income/(loss) per average common share - diluted		$ 0.91	$ 0.84
Earnings Per Share, Basic		$ 0.92	$ 0.85

[1] For the three months ended March 31, 2017, dividends were $1,000 per share for both Perpetual Preferred Stock Series A and B, $1,469 per share for Perpetual Preferred Stock Series E, and $1,406 per share for Perpetual Preferred Stock Series F.For the three months ended March 31, 2016, dividends were $1,011 per share for both Perpetual Preferred Stock Series A and B, $1,469 per share for Perpetual Preferred Stock Series E, and $1,406 per share for Perpetual Preferred Stock Series F.