Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Statement of Financial Position [Abstract]
Trading account assets pledged as collateral	$ 1,849	$ 1,239
Securities available-for-sale pledged as collateral	110	75
Fair value of securities held to maturity	$ 10,331	$ 10,720
Preferred stock, shares authorized (in shares)	5,000,000	5,000,000
Preferred stock, shares issued (in shares)	0	0
Preferred stock, shares outstanding (in shares)	0	0
Common stock, par value (dollars per share)	$ 1	$ 1
Common stock, share authorized (in shares)	1,700,000,000	1,700,000,000
Common stock, share issued (in shares)	131,935,124	131,935,124
Common stock, share outstanding (in shares)	131,935,124	131,935,124