Derivative Instruments (Cross-currency Swaps) (Details) - Cash flow hedge [Member] - Cross-currency swap contracts [Member] € in Millions, £ in Millions, SFr in Millions, $ in Millions	Dec. 31, 2017 USD ($)	Dec. 31, 2017 GBP (£)	Dec. 31, 2017 CHF (SFr)	Dec. 31, 2017 EUR (€)
2.125% 2019 euro Notes [Member]
Derivative [Line Items]
Notional amount	$ 864			€ 675
2.125% 2019 euro Notes [Member] | Euro [Member]
Derivative [Line Items]
Interest rate	2.125%	2.125%	2.125%	2.125%
2.125% 2019 euro Notes [Member] | Dollars [Member]
Derivative [Line Items]
Interest rate	2.60%	2.60%	2.60%	2.60%
1.25% 2022 euro Notes [Member]
Derivative [Line Items]
Notional amount	$ 1,388			€ 1,250
1.25% 2022 euro Notes [Member] | Euro [Member]
Derivative [Line Items]
Interest rate	1.25%	1.25%	1.25%	1.25%
1.25% 2022 euro Notes [Member] | Dollars [Member]
Derivative [Line Items]
Interest rate	3.20%	3.20%	3.20%	3.20%
0.41% 2023 Swiss franc Bonds [Member]
Derivative [Line Items]
Notional amount	$ 704		SFr 700
0.41% 2023 Swiss franc Bonds [Member] | Switzerland, Francs [Member]
Derivative [Line Items]
Interest rate	0.41%	0.41%	0.41%	0.41%
0.41% 2023 Swiss franc Bonds [Member] | Dollars [Member]
Derivative [Line Items]
Interest rate	3.40%	3.40%	3.40%	3.40%
2.00% 2026 euro Notes [Member]
Derivative [Line Items]
Notional amount	$ 833			€ 750
2.00% 2026 euro Notes [Member] | Euro [Member]
Derivative [Line Items]
Interest rate	2.00%	2.00%	2.00%	2.00%
2.00% 2026 euro Notes [Member] | Dollars [Member]
Derivative [Line Items]
Interest rate	3.90%	3.90%	3.90%	3.90%
5.50% 2026 pound sterling Notes [Member]
Derivative [Line Items]
Notional amount	$ 747	£ 475
5.50% 2026 pound sterling Notes [Member] | Sterling Pounds [Member]
Derivative [Line Items]
Interest rate	5.50%	5.50%	5.50%	5.50%
5.50% 2026 pound sterling Notes [Member] | Dollars [Member]
Derivative [Line Items]
Interest rate	6.00%	6.00%	6.00%	6.00%
4.00% 2029 pound sterling Notes [Member]
Derivative [Line Items]
Notional amount	$ 1,111	£ 700
4.00% 2029 pound sterling Notes [Member] | Sterling Pounds [Member]
Derivative [Line Items]
Interest rate	4.00%	4.00%	4.00%	4.00%
4.00% 2029 pound sterling Notes [Member] | Dollars [Member]
Derivative [Line Items]
Interest rate	4.50%	4.50%	4.50%	4.50%