Shareholders' Equity - Summary of Preferred Dividends Declared on Preferred Stock Issued (Detail) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Class of Stock [Line Items]
Total preferred stock dividends declared	$ 99	$ 96	$ 383	$ 324
Series A Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock dividends declared	$ 239.58	$ 236.98	$ 713.54	$ 710.94
Total preferred stock dividends declared	$ 7	$ 7	$ 21	$ 21
Series B Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock dividends declared	$ 387.50	$ 387.50	$ 1,162.50	$ 1,162.50
Total preferred stock dividends declared	$ 12	$ 12	$ 37	$ 37
Series C Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock dividends declared	$ 255.56	$ 252.78	$ 761.12	$ 758.34
Total preferred stock dividends declared	$ 2	$ 2	$ 6	$ 6
Series D Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock dividends declared	$ 255.56	$ 252.78	$ 761.12	$ 758.34
Total preferred stock dividends declared	$ 14	$ 14	$ 41	$ 41
Series E Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock dividends declared	$ 1,022.22	$ 1,022.22	$ 3,055.55	$ 3,044.44
Total preferred stock dividends declared	$ 12	$ 19	$ 43	$ 54
Series F Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock dividends declared	$ 1,022.22	$ 1,022.22	$ 3,055.55	$ 3,044.44
Total preferred stock dividends declared	$ 3	$ 5	$ 11	$ 15
Series I Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock dividends declared	$ 371.88	$ 371.88	$ 1,115.64	$ 1,115.64
Total preferred stock dividends declared	$ 13	$ 12	$ 38	$ 38
Series J Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock dividends declared	$ 343.75	$ 343.75	$ 1,031.25	$ 1,031.25
Total preferred stock dividends declared	$ 14	$ 14	$ 42	$ 42
Series K Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock dividends declared	$ 398.44	$ 398.44	$ 1,195.32	$ 1,195.32
Total preferred stock dividends declared	$ 11	$ 11	$ 33	$ 33
Series L Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock dividends declared			$ 712.50	$ 712.50
Total preferred stock dividends declared			$ 37	$ 37
Series M Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock dividends declared			$ 671.88
Total preferred stock dividends declared			$ 54
Series N Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock dividends declared	$ 393.75		$ 730.63
Total preferred stock dividends declared	$ 11		$ 20