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Borrowings and Credit Arrangements - Short-term Borrowings (Details) - USD ($)			12 Months Ended
	Nov. 28, 2018	Oct. 26, 2018	Dec. 31, 2019	Dec. 31, 2017	Dec. 31, 2018	Mar. 09, 2018	Dec. 15, 2017	Dec. 03, 2017
Short-term Debt [Line Items]
Short-term debt			$ 0		$ 720,000,000
Federal home loan bank advances maximum amount available			850,000,000
2018 Senior Notes
Short-term Debt [Line Items]
Debt face amount						$ 40,000,000,000
Notes Payable \| 3-Year and 5-Year Term Loan
Short-term Debt [Line Items]
Maximum borrowing capacity							$ 5,000,000,000.0
Debt face amount	$ 5,000,000,000.0
Senior Notes \| 2018 Senior Notes
Short-term Debt [Line Items]
Debt face amount						40,000,000,000.0
Commercial Paper
Short-term Debt [Line Items]
Short-term debt			0		$ 720,000,000
Short-term debt, weighted average interest rate					2.80%
Line of Credit \| Back-Up Credit Facilities
Short-term Debt [Line Items]
Short-term debt			$ 0		$ 0
Commitment fee percentage			0.03%
Line of Credit \| Revolving Credit Facility, Expiring May 14, 2020
Short-term Debt [Line Items]
Maximum borrowing capacity			$ 1,000,000,000.0
Debt instrument term			364 days
Line of Credit \| Revolving Credit Facility, Expiring May 18, 2022
Short-term Debt [Line Items]
Maximum borrowing capacity			$ 1,000,000,000.0
Debt instrument term			5 years
Line of Credit \| Revolving Credit Facility, Expiring May 17, 2023
Short-term Debt [Line Items]
Maximum borrowing capacity			$ 2,000,000,000.0
Debt instrument term			5 years
Line of Credit \| Revolving Credit Facility, Expiring May 16, 2024
Short-term Debt [Line Items]
Maximum borrowing capacity			$ 2,000,000,000.0
Debt instrument term			5 years
Bridge Loan
Short-term Debt [Line Items]
Debt instrument term		364 days
Debt face amount		$ 4,000,000,000.0				4,000,000,000.0	$ 44,000,000,000.0	$ 49,000,000,000.0
Debt issuance cost capitalized						$ 8,000,000		$ 221,000,000
Amortization of debt issuance costs			$ 173,000,000	$ 56,000,000
Extinguishment of debt	$ 4,000,000,000.0
Federal Home Loan Bank Advances
Short-term Debt [Line Items]
Short-term debt			$ 0		$ 0