Long-Term Debt - Narrative (Details) - USD ($)			12 Months Ended
	Sep. 29, 2015	Sep. 15, 2015	Dec. 31, 2017	Sep. 14, 2017	Jun. 09, 2017	Dec. 31, 2016	Nov. 22, 2016	Aug. 22, 2016	May 20, 2016	Mar. 08, 2016
Debt Instrument [Line Items]
Bank note, maximum issuable amount	$ 20,000,000,000
Senior notes available for future issuance			$ 15,800,000,000
Issuance of euro medium-term notes original maturities			Nine months or more
Senior Notes [Member]
Debt Instrument [Line Items]
Original maturity of bank note			7 days
Subordinated Notes [Member]
Debt Instrument [Line Items]
Original maturity of bank note			5 years
2.35% Senior Bank Notes due March 8, 2019 [Member]
Debt Instrument [Line Items]
Issuance of senior notes										$ 1,000,000,000
Debt instrument interest rate										2.35%
7.25% Subordinated notes due 2021 [Member]
Debt Instrument [Line Items]
Debt instrument interest rate			7.25%						3.40%
Issuance of subordinated notes			$ 348,000,000			$ 358,000,000			$ 600,000,000
1.60% Senior Bank Notes due 2019 [Member]
Debt Instrument [Line Items]
Issuance of senior notes								$ 500,000,000
Debt instrument interest rate								1.60%
2.50% Senior Notes due 2021 [Member]
Debt Instrument [Line Items]
Issuance of senior notes							$ 500,000,000
Debt instrument interest rate							2.50%
Issuance of floating rate senior notes							$ 250,000,000
2.40% Senior Bank Notes Due 2022 [Member]
Debt Instrument [Line Items]
Issuance of senior notes					$ 1,000,000,000
Debt instrument interest rate					2.40%
2.30% Senior Bank Notes Due 2022 [Member]
Debt Instrument [Line Items]
Issuance of senior notes				$ 1,000,000,000
Debt instrument interest rate				2.30%
Medium-Term Notes [Member]
Debt Instrument [Line Items]
Debt term			9 months
Issuance of medium-term notes		$ 1,000,000,000
Coupon rate of medium-term notes		2.90%
Additional debt securities authorized and available for issuance under note program			$ 4,000,000,000