Shareholders' Equity - Summary of Preferred Dividends Declared on Preferred Stock Issued (Detail) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Class of Stock [Line Items]
Total preferred stock dividends declared	$ 93	$ 96
Series A Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock dividends declared	$ 239.58	$ 239.58
Total preferred stock dividends declared	$ 7	$ 7
Series B Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock dividends declared	$ 387.50	$ 387.50
Total preferred stock dividends declared	$ 12	$ 12
Series C Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock dividends declared	$ 255.56	$ 255.56
Total preferred stock dividends declared	$ 2	$ 2
Series D Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock dividends declared	$ 255.56	$ 255.56
Total preferred stock dividends declared	$ 14	$ 14
Series E Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock dividends declared	$ 1,000.00	$ 1,011.11
Total preferred stock dividends declared	$ 7	$ 18
Series F Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock dividends declared	$ 1,000.00	$ 1,011.11
Total preferred stock dividends declared	$ 2	$ 5
Series I Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock dividends declared	$ 371.88	$ 371.88
Total preferred stock dividends declared	$ 13	$ 13
Series J Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock dividends declared	$ 343.75	$ 343.75
Total preferred stock dividends declared	$ 14	$ 14
Series K Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock dividends declared	$ 398.44	$ 398.44
Total preferred stock dividends declared	$ 11	$ 11
Series N Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock dividends declared	$ 393.75
Total preferred stock dividends declared	$ 11