Earnings Per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Earnings Per Share Table [Line Items]
Net income available to common stockholders	$ 129	$ 33	$ 416	$ 487
Basic weighted-average shares	1,023,587	826,779	893,706	825,925
Effect of dilutive securities:
Diluted weighted-average shares	1,026,504	829,368	896,322	828,150
Earnings per common share:
Basic	$ 0.13	$ 0.04	$ 0.47	$ 0.59
Diluted	$ 0.13	$ 0.04	$ 0.46	$ 0.59
Nonvested restricted stock units [Member]
Effect of dilutive securities:
Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements	2,387	1,889	2,102	1,567
Stock Options [Member]
Effect of dilutive securities:
Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements	530	700	514	658