Notes Payable, Long-Term Debt and Available Credit Facilities (Narrative) (Details) $ in Millions	1 Months Ended	9 Months Ended	36 Months Ended
	Oct. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Mar. 22, 2019	May 02, 2017 USD ($)	Jan. 31, 2017 USD ($)	Mar. 22, 2016 USD ($) borrowings
Term Loan Facility due 2019 [Member]
Schedule of Debt [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity						$ 4,500
Number of borrowings permitted | borrowings						7
Long-term Line of Credit		$ 1,000
Line of Credit Facility, Remaining Borrowing Capacity		3,500
Securities Sold under Agreements to Repurchase [Member] | Repurchase Agreements [Member]
Schedule of Debt [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity					$ 1,300
Portion of outstanding borrowing amounts required as collateral					105.00%
Line of Credit Facility, amount pledged as collateral		1,365
Short-term Debt		$ 1,300
Securities Sold under Agreements to Repurchase [Member] | Repurchase Agreements [Member] | London Interbank Offered Rate (LIBOR) [Member]
Schedule of Debt [Line Items]
Debt Instrument, basis spread on variable rate		0.75%
Senior Note 2 Point 20 Percent Due 2020 [Member]
Schedule of Debt [Line Items]
Debt Instrument, Face Amount				$ 1,250
Debt Instrument, Interest Rate, Stated Percentage				2.20%
Senior Note Floating Rate due 2020 [Member]
Schedule of Debt [Line Items]
Debt Instrument, Face Amount				$ 750
Subsequent Event [Member] | Term Loan Facility due 2019 [Member]
Schedule of Debt [Line Items]
Additional Draw - Term Loan Facility	$ 500
Scenario, Forecast [Member] | Term Loan Facility due 2019 [Member]
Schedule of Debt [Line Items]
Line of Credit Facility, expiration period			3 years