Marketable Securities and Restricted Funds Schedule of Held to Maturity Securities (Details) - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015
Schedule of Held-to-maturity Securities [Line Items]
Total held-to-maturity securities	$ 129	$ 119
Current assets—other | Bankers Acceptance
Schedule of Held-to-maturity Securities [Line Items]
Total held-to-maturity securities	44	30
Current assets—other | Canadian Government Securities
Schedule of Held-to-maturity Securities [Line Items]
Total held-to-maturity securities	25	24
Current assets—other | Money Market Funds
Schedule of Held-to-maturity Securities [Line Items]
Total held-to-maturity securities	8	3
Investments and other assets—other | Bankers Acceptance
Schedule of Held-to-maturity Securities [Line Items]
Total held-to-maturity securities	0	12
Investments and other assets—other | Canadian Government Securities
Schedule of Held-to-maturity Securities [Line Items]
Total held-to-maturity securities	$ 52	$ 50