Earnings Per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Income (Numerator):
Net income	$ 115	$ 163
Weighted average number of shares:
Weighted average shares outstanding for computing basic earnings per common share (in shares)	1,065,796	540,458
Incremental common shares attributable to dilutive securities:
Number of shares as adjusted for purposes of computing diluted earnings per common share (in shares)	1,069,183	541,522
Basic earnings per common share (in dollars per share)	$ 0.11	$ 0.30
Diluted earnings per common share (in dollars per share)	$ 0.11	$ 0.30
Common Class A
Income (Numerator):
Net income	$ 115	$ 163
Earnings applicable to non-vested restricted stock	0	0
Net income applicable to common stock for computing basic earnings per common share	115	163
Net income as adjusted for purposes of computing diluted earnings per common share	$ 115	$ 163
Weighted average number of shares:
Outstanding during period (in shares)	1,073,560	547,618
Non-vested restricted stock (in shares)	(7,764)	(7,160)
Weighted average shares outstanding for computing basic earnings per common share (in shares)	1,065,796	540,458
Incremental common shares attributable to dilutive securities:
Shares issuable under convertible securities (in shares)	10	10
Shares issuable under incentive compensation plans (in shares)	3,377	1,054
Number of shares as adjusted for purposes of computing diluted earnings per common share (in shares)	1,069,183	541,522
Basic earnings per common share (in dollars per share)	$ 0.11	$ 0.30
Diluted earnings per common share (in dollars per share)	$ 0.11	$ 0.30
Number of shares of common stock excluded from the computation of diluted earnings per share (in shares)	4,300	4,300