Preferred Stock - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended	12 Months Ended
	Jun. 30, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Class of Stock [Line Items]
Preferred stock, par value (usd per share)		$ 0
Payments for repurchase of redeemable preferred stock		$ (1,265)	$ (300)	$ 0
6.0% Non-Cumulative Preferred Stock, Series I ($1,000,000 stated value)
Class of Stock [Line Items]
Preferred stock, depositary shares outstanding (shares)	1,265,000,000
Dividend Rate		6.00%
Preferred stock, redemption price per share (usd per share)		$ 1,000,000
Floating Rate Non-Cumulative Preferred Stock, Series F ($25 stated value) [Member]
Class of Stock [Line Items]
Dividend Rate		0.00%
Preferred stock, par value (usd per share)	$ 25
14,950,000 Depositary Shares each representing a one-fortieth interest in a share of 6.50% Non-Cumulative Preferred Stock, Series H ($1,000 stated value) [Member]
Class of Stock [Line Items]
Preferred stock, depositary shares outstanding (shares)			14,950,000
Dividend Rate	6.50%	0.00%
Preferred stock, par value (usd per share)	$ 1,000
14,950,000 Depositary Shares each representing a one-fortieth interest in a share of Floating Rate Non-Cumulative Preferred Stock, Series G ($1,000 stated value) [Member]
Class of Stock [Line Items]
Preferred stock, depositary shares outstanding (shares)			14,950,000
Dividend Rate		0.00%
Preferred stock, par value (usd per share)	$ 1,000
6,000,000 Depositary shares each representing a one-fourth interest in a share of Adjustable Rate Cumulative Preferred Stock, Series D ($100 stated value) [Member]
Class of Stock [Line Items]
Preferred stock, par value (usd per share)			$ 100
$2.8575 Cumulative Preferred Stock ($50 stated value) [Member]
Class of Stock [Line Items]
Preferred stock, par value (usd per share)			50
Dividend per share (usd per share)			$ 2.8575
Preferred Stock [Member]
Class of Stock [Line Items]
Payments for repurchase of redeemable preferred stock	$ (1,265)		$ (300)
Number of shares of stock issued to parent		1,265	0	0
Preferred stock, cash consideration		$ 1,265	$ 0	$ 0
Hnah [Member] | 6.0% Non-Cumulative Preferred Stock, Series I ($1,000,000 stated value)
Class of Stock [Line Items]
Dividend Rate	6.00%
Number of shares of stock issued to parent	1,265
Preferred stock, cash consideration	$ 1,265