Debt - Schedule of Unsecured Debt (Details) - Senior Notes [Member] - USD ($)	Mar. 31, 2017	Jan. 31, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Debt instrument, face amount	$ 31,549,000,000		$ 29,008,000,000
Parent Company [Member]
Debt Instrument [Line Items]
Debt instrument, face amount		$ 2,500,000,000.0
Parent Company [Member] | 3.45% Senior Notes Due January 2022 [Member]
Debt Instrument [Line Items]
Debt instrument, face amount		1,250,000,000
Interest rate (percent)	3.45%
Parent Company [Member] | 3.45% Senior Notes Due January 2027 [Member]
Debt Instrument [Line Items]
Debt instrument, face amount		750,000,000
Interest rate (percent)	4.35%
Parent Company [Member] | Floating Rate Senior Notes Due 2022 [Member]
Debt Instrument [Line Items]
Debt instrument, face amount		$ 500,000,000