Shareholders' Equity - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Mar. 16, 2020	Dec. 06, 2019	Jul. 29, 2019
Class of Stock [Line Items]
Preferred Stock, Value, Issued					$ 2,000,000,000.0
Proceeds from Issuance of Preferred Stock and Preference Stock	$ 1,683,000,000	$ 0	$ 0
Number of shares repurchased		23,200,000	35,500,000
Repurchase of common stock		$ 1,200,000,000	$ 1,600,000,000
Preferred Stock, Value, Redeemed	(1,725,000,000)
Difference in redemption price and carrying value	$ 46,000,000
Preferred shares outstanding	145,000	126,000
Series D Preferred Stock [Member]
Class of Stock [Line Items]
Stock Redeemed or Called During Period, Shares	23,000
Series E Preferred Stock [Member]
Class of Stock [Line Items]
Stock Redeemed or Called During Period, Shares	46,000
Redeemable preferred stock
Class of Stock [Line Items]
Preferred Stock, Value, Redeemed	$ 1,700,000,000
Series K
Class of Stock [Line Items]
Dividend Rate	5.754%
Series K | Subsequent Event
Class of Stock [Line Items]
Preferred shares outstanding				5,000
Preferred Stock, Redemption Amount				$ 500,000,000
Series N
Class of Stock [Line Items]
Preferred Stock, Value, Issued						$ 1,700,000,000
Dividend Rate	4.80%
Proceeds from Issuance of Preferred Stock and Preference Stock	$ 1,700,000,000
Preferred Stock, Shares Issued	68,000