Income Taxes - Additional Information (Details) € in Millions, $ in Millions	1 Months Ended	3 Months Ended								12 Months Ended
	Dec. 31, 2017 EUR (€)	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Income Tax Disclosure [Abstract]
Provision for income taxes, net		$ 16	$ 58	$ 467	$ 229	$ 414	$ 229	$ 307	$ 475	$ 769	$ 1,425	$ 950
Cash taxes paid, net of refunds										957	412	273
Provisional tax benefit for impact of the Act										789
Income Taxes [Line Items]
Valuation allowance against the net deferred tax assets				$ 600
Net capital loss carryforwards		1,100								1,100
Accrued interest and penalties, net of federal income tax benefit, related to tax contingencies		107				$ 67				107	67
Interest and penalties, net of federal income tax benefit										40	$ 9	$ 18
State
Income Taxes [Line Items]
Net operating loss carryforwards		858								858
Federal
Income Taxes [Line Items]
Net operating loss carryforwards		226								226
Federal | IRS
Income Taxes [Line Items]
Tax examination, estimate of additional tax expense										1,500
Federal | Capital Loss Carryforward
Income Taxes [Line Items]
Net capital loss carryforwards		359								359
Foreign
Income Taxes [Line Items]
Net operating loss carryforwards		$ 8,000								$ 8,000
Foreign | Luxembourg Tax Administration
Income Taxes [Line Items]
Tax examination, estimate of additional tax expense | €	€ 250