Shareholders' Equity - Summary of Preferred Dividends Declared on Preferred Stock Issued (Detail) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Class of Stock [Line Items]
Total preferred stock dividends declared	$ 119	$ 176	$ 223	$ 265
Series A Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock dividends declared	$ 231.77	$ 236.98	$ 471.35	$ 471.36
Total preferred stock dividends declared	$ 7	$ 7	$ 14	$ 14
Series C Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock dividends declared	$ 247.22	$ 252.78	$ 502.78	$ 502.78
Total preferred stock dividends declared	$ 2	$ 2	$ 4	$ 4
Series D Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock dividends declared	$ 247.22	$ 252.78	$ 502.78	$ 502.78
Total preferred stock dividends declared	$ 13	$ 14	$ 27	$ 27
Series E Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock dividends declared	$ 1,022.22	$ 1,011.11	$ 2,022.22	$ 2,022.22
Total preferred stock dividends declared	$ 8	$ 8	$ 15	$ 15
Series F Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock dividends declared	$ 1,022.22	$ 1,011.11	$ 2,022.22	$ 2,022.22
Total preferred stock dividends declared	$ 1	$ 1	$ 3	$ 3
Series J Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock dividends declared	$ 343.75	$ 343.75	$ 687.50	$ 687.50
Total preferred stock dividends declared	$ 13	$ 14	$ 27	$ 28
Series K Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock dividends declared	$ 398.44	$ 398.44	$ 796.88	$ 796.88
Total preferred stock dividends declared	$ 11	$ 11	$ 22	$ 22
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		$ 671.88		$ 671.88
Total preferred stock dividends declared		$ 54		$ 54
Series N Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock dividends declared	$ 393.75	$ 393.75	$ 787.50	$ 787.50
Total preferred stock dividends declared	$ 9	$ 10	$ 19	$ 21
Series O Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock dividends declared	$ 662.50	$ 662.50	$ 662.50	$ 662.50
Total preferred stock dividends declared	$ 17	$ 17	$ 17	$ 17
Series P Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock dividends declared	$ 625.00	$ 625.00	$ 625.00	$ 625.00
Total preferred stock dividends declared	$ 38	$ 38	$ 38	$ 38
Series Q Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock dividends declared			$ 687.50	$ 889.93
Total preferred stock dividends declared			$ 14	$ 18
Series R Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock dividends declared			$ 618.75
Total preferred stock dividends declared			$ 15
Series S Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock dividends declared			$ 550.00
Total preferred stock dividends declared			$ 8