Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Statement of Financial Position [Abstract]
Debt Securities, Trading, Restricted	$ 884	$ 887
Debt Securities, Available-for-sale, Restricted	228	142
Fair value of securities held to maturity	$ 9,185	$ 9,508
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)	132,076,912	132,076,912
Common stock, share outstanding (in shares)	132,076,912	132,076,912