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, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Class of Stock [Line Items]
Total preferred stock dividends declared	$ 134	$ 84	$ 399	$ 369
Series A Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock dividends declared	$ 236.98	$ 244.79	$ 708.34	$ 708.34
Total preferred stock dividends declared	$ 7	$ 7	$ 21	$ 21
Series B Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock dividends declared				$ 775.00
Total preferred stock dividends declared				$ 5
Series C Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock dividends declared	$ 252.78	$ 261.11	$ 755.56	$ 755.55
Total preferred stock dividends declared	$ 2	$ 2	$ 6	$ 6
Series D Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock dividends declared	$ 252.78	$ 261.11	$ 755.56	$ 755.55
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	$ 3,044.44	$ 3,044.44
Total preferred stock dividends declared	$ 8	$ 8	$ 23	$ 23
Series F Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock dividends declared	$ 1,022.22	$ 1,022.22	$ 3,044.44	$ 3,044.44
Total preferred stock dividends declared	$ 2	$ 2	$ 5	$ 5
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	$ 13	$ 13	$ 41	$ 41
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		$ 419.68	$ 361.54	$ 1,132.18
Total preferred stock dividends declared		$ 16	$ 4	$ 53
Series M Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock dividends declared	$ 279.17		$ 951.05	$ 671.88
Total preferred stock dividends declared	$ 22		$ 76	$ 54
Series N Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock dividends declared	$ 393.75	$ 393.75	$ 1,181.25	$ 1,181.25
Total preferred stock dividends declared	$ 11	$ 11	$ 32	$ 32
Series O Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock dividends declared			$ 662.50	$ 662.50
Total preferred stock dividends declared			$ 17	$ 17
Series P Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock dividends declared			$ 625.00	$ 625.00
Total preferred stock dividends declared			$ 38	$ 38
Series Q Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock dividends declared	$ 687.50		$ 1,577.43
Total preferred stock dividends declared	$ 14		$ 32
Series R Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock dividends declared	$ 910.94		$ 910.94
Total preferred stock dividends declared	$ 22		$ 22
Series S Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock dividends declared	$ 586.67		$ 586.67
Total preferred stock dividends declared	$ 8		$ 8