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, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Class of Stock [Line Items]
Total preferred stock dividends declared	$ 94	$ 134	$ 317	$ 399
Series A Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock dividends declared	$ 239.58	$ 236.98	$ 710.93	$ 708.34
Total preferred stock dividends declared	$ 7	$ 7	$ 21	$ 21
Series C Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock dividends declared	$ 255.56	$ 252.78	$ 758.34	$ 755.56
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	$ 758.34	$ 755.56
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	$ 14	$ 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				$ 361.54
Total preferred stock dividends declared				$ 4
Series M Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock dividends declared		$ 279.17		$ 951.05
Total preferred stock dividends declared		$ 22		$ 76
Series N Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock dividends declared		$ 393.75	$ 787.50	$ 1,181.25
Total preferred stock dividends declared		$ 11	$ 19	$ 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	$ 687.50	$ 1,375.00	$ 1,577.43
Total preferred stock dividends declared	$ 14	$ 14	$ 28	$ 32
Series R Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock dividends declared	$ 618.75	$ 910.94	$ 1,237.50	$ 910.94
Total preferred stock dividends declared	$ 15	$ 22	$ 30	$ 22
Series S Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock dividends declared	$ 550.00	$ 586.67	$ 1,100.00	$ 586.67
Total preferred stock dividends declared	$ 7	$ 8	$ 15	$ 8