Shareholders' Equity - Summary of Preferred Dividends Declared on Preferred Stock Issued (Detail) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Class of Stock [Line Items]
Total preferred stock dividends declared	$ 543	$ 560	$ 584
Series A Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock dividends declared	$ 947.92	$ 947.92	$ 958.33
Total preferred stock dividends declared	$ 28	$ 28	$ 29
Series B Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock dividends declared	$ 0	$ 775.00	$ 1,550.00
Total preferred stock dividends declared		$ 5	$ 19
Series C Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock dividends declared	$ 1,011.12	$ 1,011.11	$ 1,022.23
Total preferred stock dividends declared	$ 8	$ 8	$ 8
Series D Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock dividends declared	$ 1,011.12	$ 1,011.11	$ 1,022.23
Total preferred stock dividends declared	$ 55	$ 54	$ 55
Series E Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock dividends declared	$ 4,055.55	$ 4,044.44	$ 4,077.78
Total preferred stock dividends declared	$ 31	$ 31	$ 31
Series F Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock dividends declared	$ 4,055.55	$ 4,044.44	$ 4,077.78
Total preferred stock dividends declared	$ 6	$ 7	$ 7
Series J Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock dividends declared	$ 1,375.00	$ 1,375.00	$ 1,375.00
Total preferred stock dividends declared	$ 55	$ 55	$ 55
Series K Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock dividends declared	$ 1,593.76	$ 1,593.76	$ 1,593.76
Total preferred stock dividends declared	$ 45	$ 45	$ 45
Series L Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock dividends declared	$ 361.54	$ 1,519.67	$ 1,425.00
Total preferred stock dividends declared	$ 4	$ 68	$ 74
Series M Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock dividends declared	$ 1,217.16	$ 1,343.76	$ 1,343.76
Total preferred stock dividends declared	$ 97	$ 107	$ 107
Series N Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock dividends declared	$ 1,575.00	$ 1,575.00	$ 1,575.00
Total preferred stock dividends declared	$ 43	$ 43	$ 43
Series O Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock dividends declared	$ 1,325.00	$ 1,325.00	$ 1,325.00
Total preferred stock dividends declared	$ 34	$ 34	$ 34
Series P Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock dividends declared	$ 1,250.00	$ 1,250.00	$ 1,281.25
Total preferred stock dividends declared	$ 75	$ 75	$ 77
Series Q Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock dividends declared	$ 1,577.43
Total preferred stock dividends declared	$ 32
Series R Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock dividends declared	$ 910.94
Total preferred stock dividends declared	$ 22
Series S Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock dividends declared	$ 586.67
Total preferred stock dividends declared	$ 8