Shareholders' Equity - Summary of Perpetual Preferred Stock Issued and Outstanding (Detail) $ / shares in Units, $ in Millions	9 Months Ended
	Sep. 30, 2016 USD ($) $ / shares shares
Class of Stock [Line Items]
Shares Authorized	509,250
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
Liquidation Preference | $ / shares	$ 25,000
Redemption Value | $	$ 750
Dividend Rate	3 month LIBOR + 0.75%, with floor of 3.75% per annum
Series B Preferred Stock [Member]
Class of Stock [Line Items]
Shares Authorized	50,000
Shares Issued	32,000
Shares Outstanding	32,000
Depositary Shares Per Share	1,000
Liquidation Preference | $ / shares	$ 25,000
Redemption Value | $	$ 800
Dividend Rate	6.20% per annum
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
Liquidation Preference | $ / shares	$ 25,000
Redemption Value | $	$ 200
Dividend Rate	3 month LIBOR + 0.75%, with floor of 4.00% per annum
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
Liquidation Preference | $ / shares	$ 25,000
Redemption Value | $	$ 1,350
Dividend Rate	3 month LIBOR + 0.67%, with floor of 4.00% per annum
Series E Preferred Stock [Member]
Class of Stock [Line Items]
Shares Authorized	17,500
Shares Issued	7,667
Shares Outstanding	7,667
Liquidation Preference | $ / shares	$ 100,000
Redemption Value | $	$ 767
Dividend Rate	3 month LIBOR + 0.77%, with floor of 4.00% per annum
Series F Preferred Stock [Member]
Class of Stock [Line Items]
Shares Authorized	5,000
Shares Issued	1,615
Shares Outstanding	1,615
Liquidation Preference | $ / shares	$ 100,000
Redemption Value | $	$ 161
Dividend Rate	3 month LIBOR + 0.77%, with floor of 4.00% per annum
Series I Preferred Stock [Member]
Class of Stock [Line Items]
Shares Authorized	34,500
Shares Issued	34,000
Shares Outstanding	34,000
Depositary Shares Per Share	1,000
Liquidation Preference | $ / shares	$ 25,000
Redemption Value | $	$ 850
Dividend Rate	5.95% per annum
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
Liquidation Preference | $ / shares	$ 25,000
Redemption Value | $	$ 1,000
Dividend Rate	5.50% per annum to, but excluding, May 10, 2023; 3 month LIBOR + 3.64% per annum thereafter
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
Liquidation Preference | $ / shares	$ 25,000
Redemption Value | $	$ 700
Dividend Rate	6.375% per annum to, but excluding, May 10, 2024; 3 month LIBOR + 3.55% per annum thereafter
Series L Preferred Stock [Member]
Class of Stock [Line Items]
Shares Authorized	52,000
Shares Issued	52,000
Shares Outstanding	52,000
Depositary Shares Per Share	25
Liquidation Preference | $ / shares	$ 25,000
Redemption Value | $	$ 1,300
Dividend Rate	5.70% per annum to, but excluding, May 10, 2019; 3 month LIBOR + 3.884% per annum thereafter
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
Liquidation Preference | $ / shares	$ 25,000
Redemption Value | $	$ 2,000
Dividend Rate	5.375% per annum to, but excluding, May 10, 2020; 3 month LIBOR + 3.922% per annum thereafter
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
Liquidation Preference | $ / shares	$ 25,000
Redemption Value | $	$ 675
Dividend Rate	6.30% per annum
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
Liquidation Preference | $ / shares	$ 25,000
Redemption Value | $	$ 650
Dividend Rate	5.30% per annum to, but excluding, November 10, 2026 3 month LIBOR + 3.834% per annum thereafter