Shareholders' Equity - Summary of Perpetual Preferred Stock Issued and Outstanding (Detail) $ / shares in Units, $ in Millions	9 Months Ended
	Sep. 30, 2020 USD ($) $ / shares shares
Class of Stock [Line Items]
Shares Authorized	496,750
Shares Issued	420,282
Shares Outstanding	420,280
Redemption Value | $	$ 11,203
Series A Preferred Stock [Member]
Class of Stock [Line Items]
Shares Authorized	50,000
Shares Issued	30,000
Shares Outstanding	29,999
Depositary Shares Per Share	1,000
Earliest Redemption Date	Currently redeemable
Liquidation Preference | $ / shares	$ 25,000
Redemption Value | $	$ 750
Dividend rate	3 month LIBOR + 0.75%, with floor of 3.75%, payable quarterly
Series C Preferred Stock [Member]
Class of Stock [Line Items]
Shares Authorized	25,000
Shares Issued	8,000
Shares Outstanding	8,000
Depositary Shares Per Share	1,000
Earliest Redemption Date	Currently redeemable
Liquidation Preference | $ / shares	$ 25,000
Redemption Value | $	$ 200
Dividend rate	3 month LIBOR + 0.75%, with floor of 4.00%, payable quarterly
Series D Preferred Stock [Member]
Class of Stock [Line Items]
Shares Authorized	60,000
Shares Issued	54,000
Shares Outstanding	53,999
Depositary Shares Per Share	1,000
Earliest Redemption Date	Currently redeemable
Liquidation Preference | $ / shares	$ 25,000
Redemption Value | $	$ 1,350
Dividend rate	3 month LIBOR + 0.67%, with floor of 4.00%, payable quarterly
Series E Preferred Stock [Member]
Class of Stock [Line Items]
Shares Authorized	17,500
Shares Issued	7,667
Shares Outstanding	7,667
Earliest Redemption Date	Currently redeemable
Liquidation Preference | $ / shares	$ 100,000
Redemption Value | $	$ 767
Dividend rate	3 month LIBOR + 0.7675%, with floor of 4.00%, payable quarterly
Series F Preferred Stock [Member]
Class of Stock [Line Items]
Shares Authorized	5,000
Shares Issued	1,615
Shares Outstanding	1,615
Earliest Redemption Date	Currently redeemable
Liquidation Preference | $ / shares	$ 100,000
Redemption Value | $	$ 161
Dividend rate	3 month LIBOR + 0.77%, with floor of 4.00%, payable quarterly
Series J Preferred Stock [Member]
Class of Stock [Line Items]
Shares Authorized	46,000
Shares Issued	40,000
Shares Outstanding	40,000
Depositary Shares Per Share	1,000
Earliest Redemption Date	May 10, 2023
Liquidation Preference | $ / shares	$ 25,000
Redemption Value | $	$ 1,000
Dividend rate	5.50% to, but excluding, May 10, 2023; 3 month LIBOR + 3.64% thereafter, payable quarterly
Series K Preferred Stock [Member]
Class of Stock [Line Items]
Shares Authorized	32,200
Shares Issued	28,000
Shares Outstanding	28,000
Depositary Shares Per Share	1,000
Earliest Redemption Date	May 10, 2024
Liquidation Preference | $ / shares	$ 25,000
Redemption Value | $	$ 700
Dividend rate	6.375% to, but excluding, May 10, 2024; 3 month LIBOR + 3.55% thereafter, payable quarterly
Series M Preferred Stock [Member]
Class of Stock [Line Items]
Shares Authorized	80,000
Shares Issued	80,000
Shares Outstanding	80,000
Depositary Shares Per Share	25
Earliest Redemption Date	Currently redeemable
Liquidation Preference | $ / shares	$ 25,000
Redemption Value | $	$ 2,000
Dividend rate	3 month LIBOR + 3.922%, payable quarterly
Series N Preferred Stock [Member]
Class of Stock [Line Items]
Shares Authorized	31,050
Shares Issued	27,000
Shares Outstanding	27,000
Depositary Shares Per Share	1,000
Earliest Redemption Date	May 10, 2021
Liquidation Preference | $ / shares	$ 25,000
Redemption Value | $	$ 675
Dividend rate	6.30%, payable quarterly
Series O Preferred Stock [Member]
Class of Stock [Line Items]
Shares Authorized	26,000
Shares Issued	26,000
Shares Outstanding	26,000
Depositary Shares Per Share	25
Earliest Redemption Date	Nov. 10, 2026
Liquidation Preference | $ / shares	$ 25,000
Redemption Value | $	$ 650
Dividend rate	5.30%, payable semi-annually, from issuance date to, but excluding, November 10, 2026; 3 month LIBOR + 3.834%, payable quarterly, thereafter
Series P Preferred Stock [Member]
Class of Stock [Line Items]
Shares Authorized	66,000
Shares Issued	60,000
Shares Outstanding	60,000
Depositary Shares Per Share	25
Earliest Redemption Date	Nov. 10, 2022
Liquidation Preference | $ / shares	$ 25,000
Redemption Value | $	$ 1,500
Dividend rate	5.00%, payable semi-annually, from issuance date to, but excluding, November 10, 2022; 3 month LIBOR + 2.874%, payable quarterly, thereafter
Series Q Preferred Stock [Member]
Class of Stock [Line Items]
Shares Authorized	20,000
Shares Issued	20,000
Shares Outstanding	20,000
Depositary Shares Per Share	25
Earliest Redemption Date	Aug. 10, 2024
Liquidation Preference | $ / shares	$ 25,000
Redemption Value | $	$ 500
Dividend rate	5.50%, payable semi-annually, from issuance date to, but excluding, August 10, 2024; 5 year treasury rate + 3.623%, payable semi-annually, thereafter
Series R Preferred Stock [Member]
Class of Stock [Line Items]
Shares Authorized	24,000
Shares Issued	24,000
Shares Outstanding	24,000
Depositary Shares Per Share	25
Earliest Redemption Date	Feb. 10, 2025
Liquidation Preference | $ / shares	$ 25,000
Redemption Value | $	$ 600
Dividend rate	4.95%, payable semi-annually, from issuance date to, but excluding, February 10, 2025; 5 year treasury rate + 3.224%, payable semi-annually, thereafter
Series S Preferred Stock [Member]
Class of Stock [Line Items]
Shares Authorized	14,000
Shares Issued	14,000
Shares Outstanding	14,000
Depositary Shares Per Share	25
Earliest Redemption Date	Feb. 10, 2025
Liquidation Preference | $ / shares	$ 25,000
Redemption Value | $	$ 350
Dividend rate	4.40%, payable semi-annually, from issuance date to, but excluding, February 10, 2025; 5 year treasury rate + 2.85%, payable semi-annually thereafter